Avoid using _FInf etc. in numeric_limits.h after MSVC's STL removes them

[StephanTLavavej]

I work on the Visual C++ team, where we regularly build many open-source projects, including EASTL, with development builds of the MSVC compiler and libraries, in order to prevent regressions that would affect projects. This also allows us to provide advance notice of breaking changes, such as this one:

We've merged microsoft/STL#2828, which is removing the declarations of the _FInf etc. variables from our headers. This change will ship in VS 2022 17.4 Preview 2, and it breaks EASTL because MSVC's STL still defines _CPPLIB_VER (identifying ourselves as Dinkumware-derived sources).

This PR uses our supported macro _MSVC_STL_UPDATE for identifying the updated versions of MSVC's STL, and instead uses the compiler's __builtin_huge_valf() etc. intrinsics, plus FLT_TRUE_MIN etc. from the UCRT.

These intrinsics and macros have been available for quite some time. Note that they will improve codegen, as they produce constants that are known to the compiler. In contrast, the old internal variables are separately compiled (and modifiable!), which inhibits optimizations like constant propagation.

[grojo-ea]

Hi @StephanTLavavej, thank you very much for brining this to our attention and for the PR with the fix.

We'd like to take this PR but it looks like we don't have a Contributor License Agreement for you on file yet. Do you mind filling out this form so we can merge this and any future PRs that you author?

Thanks again.

[StephanTLavavej]

@grojo-ea Done, thanks!