Clang should warn when building with `-fexperimental-bounds-safety` and `-x assembler-with-cpp`

[delcypher]

In #70480 the -fexperimental-bounds-safety flag was added.

Currently Clang will emit a warning that -fexperimental-bounds-safety is ignored when building with -x assembler. However, it won't emit a warning when building with -x assembler-with-cpp.

This issue tracks adding a warning to detect when -fexperimental-bounds-safety is used with -x assembler-with-cpp.

We can either have a generic warning whenever this combination of flags are used. Or we could have a more targeted warning:

E.g.

#if __has_feature(bounds_safety) // Should warn here
mov x0, #42
#else
#error "oh no"
#endif

rdar://117917700

[rapidsna]

We should have a targeted warning and in general follow how options are normally handled with -x assembler-with-cpp by default, in order to not introduce disruption for project builds that pass cflags to assembly.

[rapidsna]

And this targeted warning should be disabled when we actually support the feature for assembler-with-cpp to allow #if __has_feature(bounds_safety).