To simplify the win32/msvc build of I have patched glib/gspawn-win32-helper.c to always include main() and WinMain() bodies. This way only one object file is needed and the console/windows switch just needs to be done at the link step.
Would this change be ok with the mingw build, too?

diff --git a/glib/gspawn-win32-helper.c b/glib/gspawn-win32-helper.c
index 40108bb..cf25bb8 100644
--- a/glib/gspawn-win32-helper.c
+++ b/glib/gspawn-win32-helper.c
@@ -147,16 +147,8 @@ protect_wargv (wchar_t  **wargv,
   return argc;
 }
 
-#ifndef HELPER_CONSOLE
-int _stdcall
-WinMain (struct HINSTANCE__ *hInstance,
-	 struct HINSTANCE__ *hPrevInstance,
-	 char               *lpszCmdLine,
-	 int                 nCmdShow)
-#else
 int
 main (int ignored_argc, char **ignored_argv)
-#endif
 {
   int child_err_report_fd = -1;
   int helper_sync_fd = -1;
@@ -331,3 +323,13 @@ main (int ignored_argc, char **ignored_argv)
 
   return 0;
 }
+
+/* it is not the existence of this function to dediced over console/windows, just one bit set by /subsystem:? */
+int _stdcall
+WinMain (struct HINSTANCE__ *hInstance,
+	 struct HINSTANCE__ *hPrevInstance,
+	 char               *lpszCmdLine,
+	 int                 nCmdShow)
+{
+  return main(__argc, __argv);
+}