Undo include order work-around in Regex.cpp

[hans]

Summary

r327256 / 2b8b90a7686858b1d22cae6fcfbd0904135112aa added this
include-order work-around since regex_impl.h's include guard conflicted
with macOS's xlocale.h which used the same macro.

Since b86c249691a7973a451bc6a586b39da64778d219 renamed the include
guard, that work-around is no longer needed.

[JDevlieghere]

In D150117#4326737, @thakis wrote:

JDevlieghere, do you remember why you went with that other approach?

I don't remember. My best guess is that was probably trying to avoid modifying regex_impl.h because it is/was a verbatim copy of the BSD regex implementation. This is definitely better.

llvm/lib/Support/Regex.cpp

 //===-- Regex.cpp - Regular Expression matcher implementation -------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements a POSIX regular expression matcher.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/Regex.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
+#include "regex_impl.h"
+
 #include <cassert>
 #include <string>
 
-// Important this comes last because it defines "_REGEX_H_". At least on
-// Darwin, if included before any header that (transitively) includes
-// xlocale.h, this will cause trouble, because of missing regex-related types.
-#include "regex_impl.h"
-
 using namespace llvm;
 
 Regex::Regex() : preg(nullptr), error(REG_BADPAT) {}
 
 Regex::Regex(StringRef regex, RegexFlags Flags) {
   unsigned flags = 0;
   preg = new llvm_regex();
   preg->re_endp = regex.end();