…_RUN rather than the changing the global variable. Added global definition.

…vity of the filename ("cl.exe" and "CL.EXE"). First check vc_dir/bin/cl.exe and vc_dir/cl.exe for existence. Modify the vc_dir walk to check for existence under the directories rather than testing if cl.exe is in the file list. Existence test is not sensitive to file name case.

…a missing "14.Exp" key in the _VCVER_TO_VSWHERE_VER dictionary. Add the "14.Exp" to the dictionary.

…eliable when multiple versions of msvc are installed. Modify the vswhere queries by version to detect the appropriate products: 14.2 [default, BuildTools], 14.1 [default, BuildTools], 14.1Exp [WDExpress]. The default is Enterprise, Professional, Community. The order is unknown. With only Build Tools installed, 14.2 and 14.1 require two calls to vswhere.

…e may be more iterations (artifact from moving the vswhere query in a loop)