add STL4038 prefix to "requires C++NN or later" messages

[fsb4000]

Fixes #155

[strega-nil-ms]

Thanks much!

[StephanTLavavej]

Thanks, this looks good! I pushed a conflict-free merge with main, verified that we haven't added any headers that need to be updated, and pushed minor changes. The most significant change was using a new number for <coroutine>'s message about not being compatible with legacy /await, and emitting that multi-sentence message on a single line. Now its messages look like this to users:

D:\GitHub\STL>type meow.cpp
#include <coroutine>

D:\GitHub\STL>cl /EHsc /nologo /W4 /std:c++14 /c meow.cpp
meow.cpp
D:\GitHub\STL\out\build\x64\out\inc\coroutine(22): warning STL4038: The contents of <coroutine> are available only with C++20 or later or /await:strict.

D:\GitHub\STL>cl /EHsc /nologo /W4 /std:c++14 /await /c meow.cpp
meow.cpp
D:\GitHub\STL\out\build\x64\out\inc\coroutine(17): warning STL4039: The contents of <coroutine> are not available with /await. Remove /await or use /await:strict for standard coroutines. Use <experimental/coroutine> for legacy /await support.

FYI @strega-nil-ms as I pushed this after you approved; I believe it should be non-controversial but please meow if you have concerns.

[strega-nil-ms]

@StephanTLavavej LGTM!

[StephanTLavavej]

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

[StephanTLavavej]

Thanks for making these messages easier to document and look up! 😸 📖 💡

[CaseyCarter]

Thanks for making these messages easier to document and look up! 😸 📖 💡

STL4038Thanks!