<ciso646> is removed in C++20

[fsb4000]

https://en.cppreference.com/w/cpp/header

<ciso646> wasn't deprecated in C++17, this is why <ciso646> doesn't have a similar warning like <cstdbool> and other have.

#2583 uses STL4034 and STL4035

so this PR is expected to be merged after 2583

llvm-project\libcxx\test\support\test_macros.h has #include <ciso646> . This is why we need #define _SILENCE_CXX20_CISO646_REMOVED_WARNING for P0088R3_variant/test.cpp ,P0220R1_any/test.cpp and P0220R1_optional/test.cpp

https://github.com/llvm/llvm-project/blob/b8d38e8b4fcab071c5c4cb698e154023d06de69e/libcxx/test/support/test_macros.h#L23

[CaseyCarter]

I suspect there is code in the wild building with /std:c++20 /permissive that includes <ciso646> to get the macro definitions of the "alternative tokens" (and, not, etc.) which will be broken by this, but I'm comfortable given there's an escape hatch.

[StephanTLavavej]

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

[StephanTLavavej]

Merged with main:

• Adjacent deprecation warnings in <yvals_core.h>. The <ciso646> warning is now STL4036 and STL4037 is the next warning number.
• Adjacent silencing in P0088R3_variant/test.cpp. Accepted both, sorted the silencing.

[StephanTLavavej]

Thanks for implementing this removal and helping to modernize this part of the ecosystem!

😻 🚀 🧑‍🚀