libclang: introduce cxstring::{createRef,createDup} for C strings

Also migrate all clients from the old API.

llvm-svn: 174238
diff --git a/clang/tools/libclang/CXSourceLocation.cpp b/clang/tools/libclang/CXSourceLocation.cpp
index afbac6d..f29f6b4 100644
--- a/clang/tools/libclang/CXSourceLocation.cpp
+++ b/clang/tools/libclang/CXSourceLocation.cpp
@@ -263,7 +263,7 @@
     PresumedLoc PreLoc = SM.getPresumedLoc(Loc);
     
     if (filename)
-      *filename = createCXString(PreLoc.getFilename());
+      *filename = cxstring::createRef(PreLoc.getFilename());
     if (line)
       *line = PreLoc.getLine();
     if (column)