build: do not use shell calls to export empty opkg control files, speeds up...

build: do not use shell calls to export empty opkg control files, speeds up package build and fixes some "Argument list too long" errors Patch by Thomas Langer from #8450

SVN-Revision: 26431

include/package-ipkg.mk

@@ -28,8 +28,10 @@ IPKG_BUILD:= \
 IPKG_STATE_DIR:=$(TARGET_DIR)/usr/lib/opkg
 
 define BuildIPKGVariable
+ifdef Package/$(1)/$(2)
   $(call shexport,Package/$(1)/$(2))
   $(1)_COMMANDS += $(SH_FUNC) var2file "$(call shvar,Package/$(1)/$(2))" $(2);
+endif
 endef
 
 PARENL :=(