compilers-fortran: Fix preprocessing when fortran uses concat operator

[AndrewLister-STFC]

Fixes #14695

This fixes preprocessing in fortran where code uses the concatenation operator. It also fixes preprocessing when compiling with ifx.

Note on the testing:

• The test is currently failing as I don't now how to check the output of the compiled program via the project tests.
• Is it possible to add ifx as a compiler for this test to avoid a regression on this?

Any help or pointers for these notes would be appreciated!

[dcbaker]

If you want to use a printed message then you'll need a python wrapper to do the comparison. An easier approach would be to have the program exit 0 if you got the expected define, otherwise 1, since test() can easily test return codes.

[dcbaker]

If we can't handle this via the language map, I think I'd prefer to just add an overriding implementation to the GnuFortran class that simply does return self.get_preprocess_only_args() than special case fortran here, unless that makes for lots of duplication in leaf classes.

[AndrewLister-STFC]

Looks like GNULikeCompiler is a mixin for these classes. Happy to override in these classes if you prefer:

• ClassicFlangFortranCompiler
• LlvmFlangFortranCompiler
• ElbrusFortranCompiler
• GnuFortranCompiler
• IntelFortranCompiler

I can test that this is an issue on the final 2 and verify it's fixed. For the other 3, I can leave them as they are or update without testing (unless that's done by CI?).

[AndrewLister-STFC]

I suppose this could be in the language map if we had something like:

gnu_lang_map = {
    'c': 'c',
    'cpp': 'c++',
    'objc': 'objective-c',
    'objcpp': 'objective-c++',
    'fortran': ''
}

def gnulike_default_include_dirs(compiler: T.Tuple[str, ...], lang: str) -> 'ImmutableListProtocol[str]':
    lang = gnu_lang_map.get(lang, '')
    if not lang:
        return []
    ...

and

        lang = gnu_lang_map.get(self.language, 'assembler-with-cpp')
        if not lang:
            return self.get_preprocess_only_args()
        return self.get_preprocess_only_args() + [f'-x{lang}']

this might be a bit more generalised though I don't know if it's better than just doing the override in the FortranCompiler subclasses... Let me know which to update to and I can make the change.