Convert StringMap to using StringRef for its APIs.
 - Yay for '-'s and simplifications!

 - I kept StringMap::GetOrCreateValue for compatibility purposes, this can
   eventually go away. Likewise the StringMapEntry Create functions still follow
   the old style.

 - NIFC.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@76888 91177308-0d34-0410-b5e6-96231b3b80d8
12 files changed