When compiling with clang, cmake only sets MSVC when using clang-cl as
it's meant as an indication of cl.exe command line compatibility.
In this case, if one is using clang++ with the ms-abi, cmake
incorrectly takes the else branch here and library detection fails.
If instead we use MSVC_VERSION, which is empty unless a compiler
with _MSC_VER set is being used, then we get the correct behaviour.
https://cmake.org/cmake/help/latest/variable/MSVC.htmlhttps://cmake.org/cmake/help/latest/variable/MSVC_VERSION.html
