Audit MSVC references in cmake files to consider clang++

[Maetveis]

There are three major compilers on Windows targeting the MSVC ABI (i.e. linking with microsofts STL etc.):

• MSVC
• clang-cl aka clang with the MSVC compatible CLI
• clang++ aka clang with gcc compatible CLI

The cmake variable MSVC is only set for the first two as it defined in terms of the CLI interface provided:

Set to true when the compiler is some version of Microsoft Visual C++ or another compiler simulating the Visual C++ cl command-line syntax.

(from cmake docs)

For many of the checks in the library its the ABI that matters not the cmdline, so check CMAKE_CXX_SIMULATE_ID too, if it is MSVC the current compiler is targeting the MSVC ABI. This handles clang++

Fixes: #1597

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[Maetveis]

I don't think the sanitizer builds failing are relevant, this shouldn't change anything on Linux and all windows jobs pass.

[dmah42]

I don't think the sanitizer builds failing are relevant, this shouldn't change anything on Linux and all windows jobs pass.

agreed. filed https://github.com/google/benchmark/issues/1670