Makefile.package.in: Makes it possible to override the default extract commands

When using GENTARGETS (or macroes depending on it), there is no way of
specifying a custom extraction procedure. When using the patch one can
simply define $(PACKAGE_NAME)_EXTRACT_CMDS which will override the
default. If non is defined it will fall back to the default extract
procedure.

An example could look like this:

=== PACKAGE BEGIN ===
FGLRX_VERSION=11-3
FGLRX_SOURCE:=ati-driver-installer-$(FGLRX_VERSION)-x86.x86_64.run
FGLRX_SITE:=http://www2.ati.com/drivers/linux/

define FGLRX_EXTRACT_CMDS
	sh $(DL_DIR)/$(FGLRX_SOURCE) --extract $(@D)
endef

$(eval $(call GENTARGETS,package,fglrx))
=== PACKAGE END ===

Signed-off-by: Allan W. Nielsen <a@awn.dk>
Cc: Allan W. Nielsen <a@awn.dk>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/Makefile.package.in

@@ -243,8 +243,7 @@ endif
 $(BUILD_DIR)/%/.stamp_extracted:
 	@$(call MESSAGE,"Extracting")
 	$(Q)mkdir -p $(@D)
-	$(Q)$(if $($(PKG)_SOURCE),$(INFLATE$(suffix $($(PKG)_SOURCE))) $(DL_DIR)/$($(PKG)_SOURCE) | \
-	$(TAR) $(TAR_STRIP_COMPONENTS)=1 -C $(@D) $(TAR_OPTIONS) -)
+	$($(PKG)_EXTRACT_CMDS)
 # some packages have messed up permissions inside
 	$(Q)chmod -R +rw $(@D)
 	$(foreach hook,$($(PKG)_POST_EXTRACT_HOOKS),$(call $(hook))$(sep))
@@ -425,6 +424,10 @@ $(2)_TARGET_UNINSTALL =		$$($(2)_DIR)/.stamp_uninstalled
 $(2)_TARGET_CLEAN =		$$($(2)_DIR)/.stamp_cleaned
 $(2)_TARGET_DIRCLEAN =		$$($(2)_DIR)/.stamp_dircleaned
 
+# default extract command
+$(2)_EXTRACT_CMDS ?= $(if $($(2)_SOURCE),$(INFLATE$(suffix $($(2)_SOURCE))) $(DL_DIR)/$($(2)_SOURCE) | \
+	$(TAR) $(TAR_STRIP_COMPONENTS)=1 -C $$($(2)_DIR) $(TAR_OPTIONS) -)
+
 # post-steps hooks
 $(2)_POST_EXTRACT_HOOKS         ?=
 $(2)_POST_PATCH_HOOKS           ?=