Certain aspects of llvm-pdbdump require language support only present in
MSVC 2013 and higher. Since this is strictly a utility, and since we hope
to drop support for MSVC 2012 soon, don't build this unless MSVC 2013 or
higher.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@227479 91177308-0d34-0410-b5e6-96231b3b80d8