mscoree: Don't return from _CorExeMain.

Testing on Windows shows that unmanaged threads do not keep the
process open after a .NET program's entry point and all .NET
foreground threads have exited.

Signed-off-by: Vincent Povirk <vincent@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>

dlls/mscoree/corruntimehost.c

@@ -1524,6 +1524,8 @@ __int32 WINAPI _CorExeMain(void)
         mono_runtime_quit();
     }
 
+    ExitProcess(exit_code);
+
     return exit_code;
 }