Incorporate suggestions by Daniel Dunbar after his review. Thanks Daniel!

Incorporate suggestions by Daniel Dunbar after his review.  Thanks Daniel!

1) Changed ValidateDwarfFileNumber() to isValidDwarfFileNumber() to be better
   named.  Since it is just a predicate and isn't actually changing any state.

2) Added a missing return in the comments for setCurrentDwarfLoc() in
   include/llvm/MC/MCContext.h for fix formatting.

3) Changed clearDwarfLocSeen() to ClearDwarfLocSeen() since it does change
   state.

4) Simplified the last test in isValidDwarfFileNumber() to just a one line
   boolean test of MCDwarfFiles[FileNumber] != 0 for the final return statement.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@115551 91177308-0d34-0410-b5e6-96231b3b80d8