patch 8.1.1301: when compiled with VIMDLL some messages are not shown

Problem:    When compiled with VIMDLL some messages are not shown.
Solution:   Set/reset gui.in_use and gui.starting as needed. (Ken Takata,
            closes #4361)
diff --git a/src/gui_w32.c b/src/gui_w32.c
index 7bea58e..69212eb 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -4827,6 +4827,10 @@
 {
     char buf[IOSIZE];
 
+# ifdef VIMDLL
+    gui.in_use = mch_is_gui_executable();
+# endif
+
     /* Can't use emsg() here, we have not finished initialisation yet. */
     vim_snprintf(buf, IOSIZE,
 	    _("E243: Argument not supported: \"-%s\"; Use the OLE version."),