Include system_error directly.

llvm-svn: 210802
diff --git a/clang/lib/Frontend/FrontendActions.cpp b/clang/lib/Frontend/FrontendActions.cpp
index 4cc73c4..5147a8a 100644
--- a/clang/lib/Frontend/FrontendActions.cpp
+++ b/clang/lib/Frontend/FrontendActions.cpp
@@ -24,8 +24,8 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/raw_ostream.h"
-#include "llvm/Support/system_error.h"
 #include <memory>
+#include <system_error>
 
 using namespace clang;