Using clang-cl.exe as a compilerPath doesn't work with clang-x64 intelliSenseMode

[sean-mcmanus]

It ends up falling back to another compiler, such as WSL.

clang-cl.exe should be treated like clang-x64 mode with -fms-extensions -- and possibly other config changes that we may not be handling currently. I believe originally, we expected clang-cl.exe to run with msvc-x64 mode (i.e. treated exactly like cl.exe, with no system include/define querying).

Originally reported at #3898 .

[Colengms]

Note: clang-cl appears to accept cl command line args, so needs to be treated as cl in regards to command line args, but treated as clang otherwise.

[sean-mcmanus]

It looks like special args can be used, such as clang-cl.exe -TP -v -E -Xclang -dM nul

[Colengms]

I believe this should be addressed, as of 0.26.3-insiders, as previously we were not probing clang-cl correctly.