Index: tools/clang/lib/Lex/HeaderSearch.cpp
===================================================================
--- tools/clang/lib/Lex/HeaderSearch.cpp
+++ tools/clang/lib/Lex/HeaderSearch.cpp
@@ -621,10 +621,7 @@
          I != E; ++I) {
       const FileEntry *Includer = *I;
       // Concatenate the requested file onto the directory.
-      // FIXME: Portability.  Filename concatenation should be in sys::Path.
-      TmpDir = Includer->getDir()->getName();
-      TmpDir.push_back('/');
-      TmpDir.append(Filename.begin(), Filename.end());
+      llvm::sys::path::append(TmpDir, Filename);
 
       // FIXME: We don't cache the result of getFileInfo across the call to
       // getFileAndSuggestModule, because it's a reference to an element of