compilers: force clang to error on unknown warning options

[tristan957]

gcc seems to error by default if an unknown warning option is passed to it:

CC=gcc meson setup build -Dc_args=-Wbad

gcc will fail in the project() call during the sanity check. clang does not currently doing that:

CC=clang meson setup build -Dc_args=-Wbad
...will continue until an actual compilation like cc.compiles()

from meson-log.txt...
Sanity check compile stderr:
warning: unknown warning option '-Wbad' [-Wunknown-warning-option]

We should error in the sanity check to notify the user as soon as possible that they have errors in their environment.

[hlinnaka]

just some trivial typos:

Suggested change

	# Force clang to fail in sanity checks if an unknwon warning option is
	# user
	# Force clang to fail in sanity checks if an unknown warning option is
	# used

[bonzini]

always_args is a pretty heavy hammer. A better choice is to call get_compiler_check_args from _sanity_check_compile_args.

Also it's probably best to take the occasion and synchronize the handling of clang (which adds the arguments in get_compiler_check_args) and clang-cl (which does it in has_arguments).

[dcbaker]

I agree with bonzini, using the sanity check args makes more sense. I'm also concerned putting it in always args is going to break builds of projects that blinding add arguments on "is linux" or "is clang"