[MIRROR] fix a bunch of runtimes (#10683)

Co-authored-by: Kashargul <144968721+Kashargul@users.noreply.github.com>

code/modules/admin/verbs/buildmode.dm

@@ -11,6 +11,8 @@
 
 #define LAST_BUILDMODE		10
 
+GLOBAL_LIST_EMPTY(active_buildmode_holders)
+
 /proc/togglebuildmode(mob/M as mob in player_list)
 	set name = "Toggle Build Mode"
 	set category = "Special Verbs"
@@ -20,7 +22,7 @@
 			M.client.buildmode = 0
 			M.client.show_popup_menus = 1
 			M.plane_holder.set_vis(VIS_BUILDMODE, FALSE)
-			for(var/obj/effect/bmode/buildholder/H)
+			for(var/obj/effect/bmode/buildholder/H in GLOB.active_buildmode_holders)
 				if(H.cl == M.client)
 					qdel(H)
 		else
@@ -205,7 +207,12 @@
 	var/copied_faction = null
 	var/warned = 0
 
+/obj/effect/bmode/buildholder/Initialize(mapload)
+	. = ..()
+	GLOB.active_buildmode_holders += src
+
 /obj/effect/bmode/buildholder/Destroy()
+	GLOB.active_buildmode_holders -= src
 	qdel(builddir)
 	builddir = null
 	qdel(buildhelp)