Don't add '-std=' options for Clang when it's simulating MSVC's cl.exe.
This should fix issue #16266 (closed).
Clang-cl outputs a warning for an ignored GNU-style argument. This patch does not add that argument for clang-cl, which follows whatever language features implemented by the Visual Studio version it is told to track.
Topic-rename: clang-cl-no-std
Edited by Brad King