libclang: introduce cxstring::{createRef,createDup} for StringRefs

Also migrate all clients from the old API.

llvm-svn: 174263
diff --git a/clang/tools/libclang/ARCMigrate.cpp b/clang/tools/libclang/ARCMigrate.cpp
index 6494083..3941794 100644
--- a/clang/tools/libclang/ARCMigrate.cpp
+++ b/clang/tools/libclang/ARCMigrate.cpp
@@ -122,13 +122,11 @@
 void clang_remap_getFilenames(CXRemapping map, unsigned index,
                               CXString *original, CXString *transformed) {
   if (original)
-    *original = cxstring::createCXString(
-                                    static_cast<Remap *>(map)->Vec[index].first,
-                                        /*DupString =*/ true);
+    *original = cxstring::createDup(
+                    static_cast<Remap *>(map)->Vec[index].first);
   if (transformed)
-    *transformed = cxstring::createCXString(
-                                   static_cast<Remap *>(map)->Vec[index].second,
-                                  /*DupString =*/ true);
+    *transformed = cxstring::createDup(
+                    static_cast<Remap *>(map)->Vec[index].second);
 }
 
 void clang_remap_dispose(CXRemapping map) {