fftw @2.1.5_9 +gfortran: Fails to build on M1 with error in configure stage

[p-bro]

Fault happens on Apple M1 running Big Sur 11.6. The relevant section in the log file is

:info:configure checking build system type... configure: error: /bin/sh ./config.sub -apple-darwin20.6.0 failed
:info:configure configure: WARNING: cache variable ac_cv_build contains a newline
:info:configure Command failed:  cd "/opt/local/var/macports/build/_opt_local_var_macports_sources_rsync.macports.org_macports_release_tarballs_ports_math_fftw/fftw/work/fftw-2.1.5" && ./configure --prefix=/opt/local --enable-type-prefix --enable-threads --enable-fortran --infodir=/opt/local/share/info --enable-shared 

I think that may be the configure file's unfamiliarity with the architecture.

As this port has no maintainer, I'm probably pretty much shouting in the void, but I'm recording it here for completeness. Full log attached.

[p-bro]

fftw build log

[reneeotten (Renee Otten)]

do you need to use the fftw port (i.e., version 2.x) or would fftw-3 also work; there is a higher likelihood that this newer version would build... perhaps.

[jmroot (Joshua Root)]

In 6ba320a2057eba4375c6f1fd135e7b38192bc0ac/macports-ports (master):

fftw: force update of autotools files

In particular this gets us a config.guess and config.sub that know
about Apple Silicon.

Fixes: #63527