Update for llvm api change.

llvm-svn: 216397
diff --git a/clang/lib/Frontend/DependencyFile.cpp b/clang/lib/Frontend/DependencyFile.cpp
index 6dbd46d..ce33086 100644
--- a/clang/lib/Frontend/DependencyFile.cpp
+++ b/clang/lib/Frontend/DependencyFile.cpp
@@ -297,11 +297,11 @@
     return;
   }
 
-  std::string Err;
-  llvm::raw_fd_ostream OS(OutputFile.c_str(), Err, llvm::sys::fs::F_Text);
-  if (!Err.empty()) {
-    PP->getDiagnostics().Report(diag::err_fe_error_opening)
-      << OutputFile << Err;
+  std::error_code EC;
+  llvm::raw_fd_ostream OS(OutputFile, EC, llvm::sys::fs::F_Text);
+  if (EC) {
+    PP->getDiagnostics().Report(diag::err_fe_error_opening) << OutputFile
+                                                            << EC.message();
     return;
   }