Revert "Fix isPodLike for MSVC and use it in TypeHashing."

This reverts commit ac5edc198eb612f82293850c3488042708b1c5fa.

Apparently this doesn't cover all the bases, so some compilers
and standard libraries still think this is not trivially copyable
even though it is.  Reverting this back to an MSVC-only check for
now so that at least we have some coverage.

llvm-svn: 320739