Makefile: glib-genmarshal: use BR2_STAGING_DIR instead of hardcoded staging_dir

Makefile

@@ -123,7 +123,7 @@ HOSTLD:=$(shell $(CONFIG_SHELL) -c "which $(HOSTLD)" || type -p $(HOSTLD) || ech
 HOSTLN:=$(shell $(CONFIG_SHELL) -c "which $(HOSTLN)" || type -p $(HOSTLN) || echo ln)
 HOSTNM:=$(shell $(CONFIG_SHELL) -c "which $(HOSTNM)" || type -p $(HOSTNM) || echo nm)
 # ignore version in staging_dir
-HOST_GLIB_BIN:=`dirname $(shell $(CONFIG_SHELL) -c "(which -a glib-genmarshal; echo /usr/bin/glib-genmarshal)|grep -v staging_dir|head -n 1")`
+HOST_GLIB_BIN:=`dirname $(shell $(CONFIG_SHELL) -c "(which -a glib-genmarshal; echo /usr/bin/glib-genmarshal)|grep -v $(BR2_STAGING_DIR)|head -n 1")`
 HOST_GLIB:=$(shell $(CONFIG_SHELL) -c "dirname $(HOST_GLIB_BIN)" || echo /usr)