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.

llvm-svn: 115551