Perform proper conversion for strings encoded in the source file as UTF-8. ...

Perform proper conversion for strings encoded in the source file as UTF-8.  (For now, we are assuming the source character set is always UTF-8; this can be easily extended if necessary.)

Tests will be coming up in a subsequent commit.

Patch by Seth Cantrell.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@143416 91177308-0d34-0410-b5e6-96231b3b80d8