build: export STAGING_DIR_HOST in toplevel make code

Fixes ncurses pkg-config check for menuconfig

Signed-off-by: Felix Fietkau <[email protected]>

include/toplevel.mk

@@ -60,6 +60,7 @@ endif
 
 SCAN_COOKIE?=$(shell echo $$$$)
 export SCAN_COOKIE
+export STAGING_DIR_HOST=$(TOPDIR)/staging_dir/host
 
 SUBMAKE:=umask 022; $(SUBMAKE)