Re: Add '-Wno-complain-wrong-lang', and use it in 'gcc/testsuite/lib/target-supports.exp:check_compile' and elsewhere (was: Make '-frust-incomplete-and-experimental-compiler-do-not-use' a 'Common' option)

[Iain Buclaw <ibuclaw@gdcproject.org>]

Excerpts from Thomas Schwinge's message of Dezember 16, 2022 3:10 pm:
> 
> In the test suites, a number of existing test cases explicitly match the
> "command-line option [...] is valid for [...] but not for [...]"
> diagnostic with 'dg-warning'; I've left those alone.  On the other hand,
> I've changed 'dg-prune-output' of this diagnostic into
> '-Wno-complain-wrong-lang' usage.  I'm happy to adjust that in either way
> anyone may prefer.  I've not looked for test cases that just to silence
> this diagnostic use more general 'dg-prune-output', 'dg-excess-errors',
> '-w', etc.
> 
> In the GCC/D test suite, I see a number of:
> 
>     cc1plus: warning: command-line option '-fpreview=in' is valid for D but not for C++
> 
>     cc1plus: warning: command-line option '-fextern-std=c++11' is valid for D but not for C++
> 
> It's not clear to me how they, despite this, do achieve
> 'PASS: [...] (test for excess errors)'?  Maybe I haven't found where that
> gets pruned/ignored?
> 

There's an implicit dg-prune-output inserted by the gdc-convert-test
proc. As the only tests that mix C++ and D sources is the runnable_cxx
part of the testsuite, I can add the flag to the D2 testsuite scripts
later just for those tests.

Iain.