Gromacs 2020.4 installerror: #error "compiling simd-avx2.h without avx2 support"

GROMACS version: 2020.4
GROMACS modification: No

System: Centos 7
gcc: 9.3
Age of system - less than a year
Has installed GROMACS before? Yes, currently runs GROMACS 2021.3 fine

A short story of how I got here: Gromacs 2021.3 has a bug causing free energy calculations to fail during decoupling. See red-mine, updated 3 weeks ago to confirm issue still exists

So I wanted to install an older version of gromacs. I tried Gromacs 2018, it failed due to conflicts with CUDA - i.e., it had errors in make due to `compute_30’

This issue with CUDA was resolved in GROMACS 2020.4, hence, now I am trying to install GROMACS 2020.4. I get the same issue as this post, but no solution to the problem
Similar to:

What I did:
cmake .. -DGMX_BUILD_OWN_FFTW=ON -DREGRESSIONTEST_DOWNLOAD=ON
followed by
make -j12
This led to

/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
/fftwBuild/dft/simd/avx2/n1fv_10.c  -fPIC -DPIC -o n1fv_10.o
libtool: compile:  /home/bkelly/psi4conda/bin/x86_64-conda-linux-gnu-cc -DHAVE_CONFIG_H -I. -I/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2 -I../../.. -I /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild -DNDEBUG -D_FORTIFY_SOURCE=2 -O2 -isystem /home/bkelly/psi4conda/include -march=core-avx2 -mfma -march=nocona -mtune=haswell -ftree-vectorize -fPIC -fstack-protector-strong -fno-plt -O2 -ffunction-sections -pipe -isystem /home/bkelly/psi4conda/include -MT n1fv_9.lo -MD -MP -MF .deps/n1fv_9.Tpo -c /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_9.c  -fPIC -DPIC -o n1fv_9.o
libtool: compile:  /home/bkelly/psi4conda/bin/x86_64-conda-linux-gnu-cc -DHAVE_CONFIG_H -I. -I/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2 -I../../.. -I /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild -DNDEBUG -D_FORTIFY_SOURCE=2 -O2 -isystem /home/bkelly/psi4conda/include -march=core-avx2 -mfma -march=nocona -mtune=haswell -ftree-vectorize -fPIC -fstack-protector-strong -fno-plt -O2 -ffunction-sections -pipe -isystem /home/bkelly/psi4conda/include -MT n1fv_8.lo -MD -MP -MF .deps/n1fv_8.Tpo -c /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_8.c  -fPIC -DPIC -o n1fv_8.o
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_2.c:71,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_2.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_12.c:150,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_12.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_4.c:82,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_4.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_3.c:78,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_3.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_7.c:115,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_7.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_11.c:183,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_11.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_10.c:138,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_10.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_13.c:229,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_13.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_8.c:114,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_8.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_6.c:99,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_6.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_5.c:98,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_5.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
In file included from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/n1f.h:21,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/../common/n1fv_9.c:160,
                 from /apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/dft/simd/avx2/n1fv_9.c:3:
/apps/gromacs-2020.4/build/src/external/build-fftw/fftwBuild-prefix/src/fftwBuild/simd-support/simd-avx2.h:43:2: error: #error "compiling simd-avx2.h without avx2 support"
   43 | #error "compiling simd-avx2.h without avx2 support"
      |  ^~~~~
make[8]: *** [Makefile:755: n1fv_10.lo] Error 1
make[8]: *** Waiting for unfinished jobs....
make[8]: *** [Makefile:755: n1fv_12.lo] Error 1
make[8]: *** [Makefile:755: n1fv_4.lo] Error 1
make[8]: *** [Makefile:755: n1fv_9.lo] Error 1
make[8]: *** [Makefile:755: n1fv_5.lo] Error 1
make[8]: *** [Makefile:755: n1fv_3.lo] Error 1
make[8]: *** [Makefile:755: n1fv_13.lo] Error 1
make[8]: *** [Makefile:755: n1fv_2.lo] Error 1
make[8]: *** [Makefile:755: n1fv_8.lo] Error 1
make[8]: *** [Makefile:755: n1fv_11.lo] Error 1
make[8]: *** [Makefile:755: n1fv_6.lo] Error 1
make[8]: *** [Makefile:755: n1fv_7.lo] Error 1
make[7]: *** [Makefile:512: all] Error 2
make[6]: *** [Makefile:395: all-recursive] Error 1
make[5]: *** [Makefile:502: all-recursive] Error 1
make[4]: *** [Makefile:708: all-recursive] Error 1
make[3]: *** [Makefile:552: all] Error 2
make[2]: *** [src/external/build-fftw/CMakeFiles/fftwBuild.dir/build.make:133: src/external/build-fftw/fftwBuild-prefix/src/fftwBuild-stamp/fftwBuild-build] Error 2
make[1]: *** [CMakeFiles/Makefile2:3556: src/external/build-fftw/CMakeFiles/fftwBuild.dir/all] Error 2
make: *** [Makefile:182: all] Error 2