Refactor C++ standard library detection into module

Move CMake scripting to perform a try_run of a program to output
C++ standard library vendor/version to dedicated CMake module
CheckCXXStandardLibrary. Only perform try_run when not cross
compiling.

TODO : investigate ability to use preprocessor pragmas/diagnostics
to determine standard library at compilation time. This would allow
the vendor/version to be determined even when cross compiling
(I think...).