patch 8.1.0743: giving error messages is not flexible

Problem:    Giving error messages is not flexible.
Solution:   Add semsg().  Change argument from "char_u *" to "char *", also
            for msg() and get rid of most MSG macros. (Ozaki Kiichi, closes
            #3302)  Also make emsg() accept a "char *" argument.  Get rid of
            an enormous number of type casts.
diff --git a/src/gui_at_sb.c b/src/gui_at_sb.c
index 1816daa..72dc8c8 100644
--- a/src/gui_at_sb.c
+++ b/src/gui_at_sb.c
@@ -485,7 +485,7 @@
 
 	if (XGetGeometry (XtDisplay(w), sbw->scrollbar.thumb, &root, &x, &y,
 		&width, &height, &bw, &depth) == 0)
-	    EMSG(_("Scrollbar Widget: Could not get geometry of thumb pixmap."));
+	    emsg(_("Scrollbar Widget: Could not get geometry of thumb pixmap."));
     }
 
     gcValues.foreground = sbw->scrollbar.foreground;