FindBoost: Consider boost suffixes suitable for clang-cl
When compiling with clang-cl
we can use either the MSVC- or Clang-built boost libraries.
This changes the way msvc prefixes are handled
Instead of only determining msvc by compiler id, it uses MSVC
variable which should be set for cl and clang-cl I believe.
In addition to that, if compiler is clang-cl we add clang's prefix with major version of compiler
Topic-rename: FindBoost-clang-cl
Edited by Brad King