rules.mk: export STAGING_DIR_HOST to sub-makefiles and shells

Certains host packages (like quilt) need to know the previously used
install location at run-time. They currently use $STAGING_DIR, which
causes issues on cleaned environment, where $STAGING_DIR doesn't exist
yet.

Signed-off-by: Mathieu Olivari <mathieu@codeaurora.org>

SVN-Revision: 47409

rules.mk

@@ -188,7 +188,7 @@ else
 endif
 
 export PATH:=$(TARGET_PATH)
-export STAGING_DIR
+export STAGING_DIR STAGING_DIR_HOST
 export SH_FUNC:=. $(INCLUDE_DIR)/shell.sh;
 
 PKG_CONFIG:=$(STAGING_DIR_HOST)/bin/pkg-config