Enable more test coverage for warning C4668 ('MEOW' is not defined as a preprocessor macro)

[StephanTLavavej]

Warning C4668 is off-by-default, but quite useful because (1) we conventionally never want to rely on the Standard's behavior of expanding not-defined macros to 0, and (2) it can detect typos. We already have some test coverage for it:

STL/stl/inc/__msvc_all_public_headers.hpp

Line 13 in 8b081e2

#pragma warning(1 : 4668) // 'MEOW' is not defined as a preprocessor macro, replacing with '0' for '#if/#elif'

However, we haven't applied this warning to our entire test suite, so I've had to catch other PRs unintentionally expanding not-defined macros.

• C4668: In std and tr1, enable warning C4668 'MEOW' is not defined as a preprocessor macro, replacing with '0' for '#if/#elif'.
  • I'm excluding libcxx because it doesn't follow our convention.
• C4668: Disable warning C4668 around <Windows.h>.
  • This works around OS-23694920 "Windows SDK uses undefined _WIN32_WINNT_* version macros (which may subtly break code)".
• C4668: Remove unnecessary inclusion of <Windows.h>.
• C4668: #if WIDE => #ifdef WIDE
  • These occurrences were inconsistent.
• C4668: Activate C99 logic in tr1/include/tdefs.h.
  • This is a behavioral change/enhancement (the code was previously inactive). It fixes "warning C4668: '__STDC_VERSION__' is not defined as a preprocessor macro, replacing with '0' for '#if/#elif'".
  • We don't usually mess with tr1, but this looks like a straightforward improvement, and it only takes effect when the "approximately equal" test is already going to fail.
• C4668: Disable warning C4668 around <limits.h>.
  • This is the only product code change, to work around VSO-1985428 "<limits.h> emits warning C4668: '__STDC_WANT_SECURE_LIB__' is not defined as a preprocessor macro, replacing with '0' for '#if/#elif'".

[StephanTLavavej]

I'm speculatively mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.