Clean up #includes.

module/regex.cxx

@@ -1,18 +1,15 @@
 
 module;
 
+#if defined(__cpp_lib_modules) || (defined(_MSC_FULL_VER) && (_MSC_FULL_VER >= 193933523))
+#define BOOST_REGEX_USE_STD_MODULE
+#endif
+
 #if defined(_WIN32) && __has_include(<windows.h>)
-//
-// This has to appear *before* import std; otherwise the compiler chokes.
-//
 #include <windows.h>
 #endif
 
-#ifdef __cpp_lib_modules
-import std;
-#elif defined(MSVC_EXPERIMENTAL_STD_MODULE)
-import std.core;
-#else
+#if !defined(BOOST_REGEX_USE_STD_MODULE) && !defined(MSVC_EXPERIMENTAL_STD_MODULE)
 #include <cassert>
 #include <cstdint>
 #include <climits>
@@ -47,10 +44,13 @@ import std.core;
 #ifdef BOOST_HAS_THREADS
 #include <mutex>
 #endif
-#endif
-
 #include <cwctype>
 #include <assert.h>
+#endif
+
+#if !defined(BOOST_REGEX_USE_STD_MODULE) && defined(MSVC_EXPERIMENTAL_STD_MODULE)
+#include <cwchar>
+#endif
 
 #if __has_include(<unicode/utypes.h>)
 #include <unicode/utypes.h>
@@ -64,6 +64,16 @@ import std.core;
 
 export module boost.regex;
 
+#if defined(BOOST_REGEX_USE_STD_MODULE)
+import std;
+#elif defined(MSVC_EXPERIMENTAL_STD_MODULE)
+import std.core;
+#endif
+
+#ifdef _MSC_FULL_VER
+#pragma warning(disable:5244)
+#endif
+
 #include <boost/regex.hpp>
 
 #if __has_include(<unicode/utypes.h>)