Safer macro restoration using MSVC extensions

src/beast/beast/nudb/win32_file.h

@@ -33,6 +33,9 @@
 #endif
 
 #if BEAST_NUDB_WIN32_FILE
+#pragma push_macro("NOMINMAX")
+#pragma push_macro("UNICODE")
+#pragma push_macro("STRICT")
 # ifndef NOMINMAX
 #  define NOMINMAX
 # endif
@@ -46,9 +49,9 @@
 #  define WIN32_LEAN_AND_MEAN
 # endif
 # include <Windows.h>
-# undef NOMINMAX
-# undef UNICODE
-# undef STRICT
+#pragma pop_macro("STRICT")
+#pragma pop_macro("UNICODE")
+#pragma pop_macro("NOMINMAX")
 #endif
 
 namespace beast {