Retrieve MSVC version from cl.exe

[bernhardmgruber]

This PR lets the ctest script retrieve the MSVC version from cl.exe instead of by compiling ./cmake/msvc_version.c, which has been deleted in #290.

[bernhardmgruber]

I see the MSVC version strings appearing in cdash :)

[amadio]

You know CMake has CMAKE_CXX_COMPILER_VERSION, right? :-)

[bernhardmgruber]

You know CMake has CMAKE_CXX_COMPILER_VERSION, right? :-)

Yes, but does it have that variable in the dashboard client script for ctest? ;-D

Edit: just tried it, the variable is empty in inside test.cmake.

[amadio]

Yeah, I forgot that I actually detect this information using cmake --system-information in veccore/cmake/TestVecCore.cmake... We can copy that piece of code for Vc's test.cmake, because that works for all compilers, not just MSVC.

[bernhardmgruber]

I would prefer my simple fix for this PR. But we can sure consider simplifying test.cmake a lot by copying from veccore in a subsequent PR.