Use std::error_code instead of llvm::error_code.

The idea of this patch is to turn llvm/Support/system_error.h into a
transitional header that just brings in the erorr_code api to the llvm
namespace. I will remove it shortly afterwards.

The cases where the general idea needed some tweaking:

* std::errc is a namespace in msvc, so we cannot use "using std::errc". I could
add an #ifdef, but there were not that many uses, so I just added std:: to
them in this patch.

* Template specialization had to be moved to the std namespace in this
patch set already.

* The msvc implementation of default_error_condition doesn't seem to
provide the same transformations as we need. Not too surprising since
the standard doesn't actually say what "equivalent" means. I fixed the
problem by keeping our old mapping and using it at error_code
construction time.

Despite these shortcomings I think this is still a good thing. Some reasons:

* The different implementations of system_error might improve over time.
* It removes 925 lines of code from llvm already.
* It removes 6313 bytes from the text segment of the clang binary when
it is built with gcc and 2816 bytes when building with clang and
libstdc++.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210687 91177308-0d34-0410-b5e6-96231b3b80d8

utils/KillTheDoctor/KillTheDoctor.cpp

@@ -43,6 +43,7 @@
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/Support/system_error.h"
 #include "llvm/Support/type_traits.h"
+#include "llvm/Support/WindowsError.h"
 #include <algorithm>
 #include <cerrno>
 #include <cstdlib>
@@ -169,9 +170,7 @@ namespace {
   typedef ScopedHandle<FileHandle>              FileScopedHandle;
 }
 
-static error_code windows_error(unsigned E) {
-  return error_code(E, system_category());
-}
+static error_code windows_error(DWORD E) { return mapWindowsError(E); }
 
 static error_code GetFileNameFromHandle(HANDLE FileHandle,
                                         std::string& Name) {
@@ -426,7 +425,7 @@ int main(int argc, char **argv) {
     if (!success) {
       ec = windows_error(::GetLastError());
 
-      if (ec == errc::timed_out) {
+      if (ec == std::errc::timed_out) {
         errs() << ToolName << ": Process timed out.\n";
         ::TerminateProcess(ProcessInfo.hProcess, -1);
         // Otherwise other stuff starts failing...