Teach Windows-cl.cmake to use CMAKE_(C|CXX)_COMPILER_VERSION to set the
"MSVC##" and MSVC_VERSION variables. It no longer needs the IDE generator
to dictate the version or to detect the version by running the
command-line tool for NMake and Ninja generators. Drop configuration of
CMakeCPlatform.cmake and CMakeCXXPlatform.cmake from Windows-cl.cmake.in
because all the results it saved are now cheap to compute every time.
Since the parent commit the local generator Version ivar may be
compared for ordering. Convert comparisons:
"==VS10" becomes ">=VS10"
"!=VS10" becomes "< VS10"
to support an explicit enumeration value for VS11 with no change
in behavior.
