remove old compatibility APIs, use StringRef versions instead.

llvm-svn: 119935
diff --git a/clang/lib/Lex/HeaderMap.cpp b/clang/lib/Lex/HeaderMap.cpp
index 5d9b218..d5d7e4b 100644
--- a/clang/lib/Lex/HeaderMap.cpp
+++ b/clang/lib/Lex/HeaderMap.cpp
@@ -225,6 +225,6 @@
     llvm::SmallString<1024> DestPath;
     DestPath += getString(B.Prefix);
     DestPath += getString(B.Suffix);
-    return FM.getFile(DestPath.begin(), DestPath.end(), FileSystemOpts);
+    return FM.getFile(DestPath.str(), FileSystemOpts);
   }
 }