fftw-3 configure error on 10.5.8 for ppc64 when using external gcc10

[barracuda156]

fftw-3 fails to configure for ppc64 with Macports gcc7 due to this problem: #64260

I have now a working gcc10 outside of Macports, which can build binaries for ppc64. Set it as default gcc and tried to use:

36-111:~ svacchanda$ export CC=/opt/iains/powerpc-apple-darwin9/gcc-10-3-ppc/bin/gcc
36-111:~ svacchanda$ export CXX=/opt/iains/powerpc-apple-darwin9/gcc-10-3-ppc/bin/g++
36-111:~ svacchanda$ which gcc
/opt/iains/powerpc-apple-darwin9/gcc-10-3-ppc/bin/gcc
36-111:~ svacchanda$ sudo port -v install fftw-3 configure.compiler=gcc supported_archs="ppc ppc64" build_arch="ppc ppc64"

However it fails now with a different error:

checking size of size_t... configure: error: in `/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_math_fftw-3/fftw-3/work/fftw-3.3.10-ppc':
configure: error: cannot compute sizeof (size_t)
See `config.log' for more details
Command failed:  cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_math_fftw-3/fftw-3/work/fftw-3.3.10-ppc" && ./configure --prefix=/opt/local --enable-threads --enable-shared --with-our-malloc --enable-fma 
Exit code: 77
Error: Failed to configure fftw-3: consult /opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_math_fftw-3/fftw-3/work/fftw-3.3.10-ppc/config.log
Error: Failed to configure fftw-3: configure failure: command execution failed
Error: See /opt/local/var/macports/logs/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_math_fftw-3/fftw-3/main.log for details.
Error: Follow https://guide.macports.org/#project.tickets if you believe there
is a bug.
Error: Processing of port fftw-3 failed

[ryandesign (Ryan Carsten Schmidt)]

Please attach the config.log so that we can see why that configure test failed.

[barracuda156]

Replying to ryandesign:

Please attach the config.log so that we can see why that configure test failed.

It looks that it just ignored and used gcc7 instead.

But @kencu strongly advised against using external compiler in Macports: ​https://github.com/iains/gcc-10-branch/issues/4#issuecomment-1008157050 So I guess I rather wait until someone either fixes Macports gcc7 so that it starts building ppc64 or implements @iains fixes of gcc10 for PowerPC from here: ​https://github.com/iains/gcc-10-branch/tree/gcc-10-3-ppc (this branch builds on PowerPC and produces both pcc and ppc64 binaries on 10.5.8).