MS format strings: support the 'w' length modifier (PR20808)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217195 91177308-0d34-0410-b5e6-96231b3b80d8
MS format strings: allow the 'h' length modifier with C, C, s and S (PR20808)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217196 91177308-0d34-0410-b5e6-96231b3b80d8