Remove system_error.h.

This is a minimal change to remove the header. I will remove the occurrences
of "using std::error_code" in a followup patch.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210803 91177308-0d34-0410-b5e6-96231b3b80d8

utils/FileCheck/FileCheck.cpp

@@ -27,11 +27,11 @@
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/SourceMgr.h"
 #include "llvm/Support/raw_ostream.h"
-#include "llvm/Support/system_error.h"
 #include <algorithm>
 #include <cctype>
 #include <map>
 #include <string>
+#include <system_error>
 #include <vector>
 using namespace llvm;