VS: Restore support for mixing C++23 and C in one target with clang-cl
Since !9818 (merged) we use a Clang-specific flag to enable C++23 since
clang-cl
has no -std:c++23
flag, and -std:c++latest
may enable an
even newer version of C++. However, in .vcxproj
files there is no way
to express a target-wide -clang:-std=c++23
flag for only C++ sources
when the target also has C sources. Add a special case to map back to
-std:c++latest
for targets with C++23 and C together.
Fixes: #26508 (closed)
Backport: release