gfortran ISO_Fortran_binding.h doesn't work with clang

[jeffhammond]

I accept that mixing clang and gfortran is not the preferred scenario, but this works on every other platform.

I haven't looked at the preprocessor stuff to figure out what is going wrong here, but I wonder if there is a way to handle this properly in the GCC headers, and not rely on the gcc driver.

In file included from /opt/homebrew/Cellar/gcc/15.1.0/lib/gcc/current/gcc/aarch64-apple-darwin24/15/include/ISO_Fortran_binding.h:33:
/opt/homebrew/Cellar/gcc/15.1.0/lib/gcc/current/gcc/aarch64-apple-darwin24/15/include/stddef.h:448:68: error: __float128 is not supported on this target
  448 |   __float128 __max_align_f128 __attribute__((__aligned__(__alignof(__float128))));
      |                                                                    

If I'm being unreasonable here, feel free to close.

[wdeconinck]

I have stumbled on the same problem with C++11 onwards, mixing clang and gfortran, and trying to explore "ISO_Fortran_binding.h"

As a workaround, when I don't add in this case "-I/opt/homebrew/Cellar/gcc/15.1.0/lib/gcc/current/gcc/aarch64-apple-darwin24/15/include" to the compiler command, but rather include the file "ISO_Fortran_binding.h" as a full path as (in this case)

#include "/opt/homebrew/Cellar/gcc/15.1.0/lib/gcc/current/gcc/aarch64-apple-darwin24/15/include/ISO_Fortran_binding.h"

then the internal include to "stddef.h" is not the GCC one which has compilation problem but rather the AppleClang one.

I guess it is now more of a challenge for the build-system (e.g. cmake) to inject this correctly to retain the portability.