Silence GCC warnings when using libc++ headers.

[jhb]

Summary

GCC 12 raises warnings about literal operator suffixes not preceded by
'_' in libc++ headers such as <string_view> as it doesn't recognize
libc++ headers being an implementation of the standard.

GCC 12 also warns about clang-specific pragmas in <locale>.

[imp]

share/mk/bsd.sys.mk

222

Any reason we want to have this for all the files in the system?

[jhb]

share/mk/bsd.sys.mk

222

Because I couldn't find a way to shut it up for "any file that #includes <string_view>" or any host of other standard headers provided by libc++. In theory we could patch all the headers in libc++ to explicitly disable this warning via #pragma push/pop but that would probably give @dim nightmares. Similarly, we could perhaps patch <locale> but I suspect that wouldn't be ideal either.

[imp]

share/mk/bsd.sys.mk

222

OK. That's a decent reason :).
Might want to mention that it's suboptimal in the commit message then

[jhb]

share/mk/bsd.sys.mk

222

That's fair.

[emaste]

share/mk/bsd.sys.mk

222

Maybe also in a comment here?

[arichardson]

I am surprised that this is needed considering libc++ has pragma GCC system_header: https://github.com/llvm/llvm-project/blame/main/libcxx/include/string_view#L240