patch 9.1.0538: not possible to assign priority when defining a sign

Problem:  not possible to assign priority when defining a sign
          (Mathias Fußenegger)
Solution: Add the priority argument for the :sign-define ex command and
          the sign_define() function (LemonBoy)

Use the specified value instead of the default one (SIGN_DEF_PRIO) when
no priority is explicitly specified in sign_place or :sign place.

fixes: #8334
closes: #15124

Signed-off-by: LemonBoy <thatlemon@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/src/popupwin.c b/src/popupwin.c
index e353272..9d60aa2 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -699,8 +699,8 @@
 
 	    if (syn_name2id((char_u *)linehl) == 0)
 		linehl = "PmenuSel";
-	    sign_define_by_name(sign_name, NULL, (char_u *)linehl,
-						       NULL, NULL, NULL, NULL);
+	    sign_define_by_name(sign_name, NULL, (char_u *)linehl, NULL, NULL, NULL,
+		    NULL, SIGN_DEF_PRIO);
 	}
 
 	sign_place(&sign_id, (char_u *)"PopUpMenu", sign_name,