Add fallback for detecting CPU speed from Windows registry on builds where...

Add fallback for detecting CPU speed from Windows registry on builds where USE_ASM_INSTRUCTIONS gets defined to 0. (Win64 builds.) Clean up methods to return false when not implemented or when they fail to detect the things they're supposed to detect. This file still needs a lot more work to have a fully working implementation on Win64 builds. Committing it now because it's slightly better than it was, and there is a need for the CPU speed detection code in projects that depend on kwsys. Will file a bug shortly to request that the missing implementations get filled in...