build: SDK/IB reproducible and faster compression

Both IB and SDK now use the same logic for packing.

This commit add reproducible multithread compression to the SDK and
corrects the file mtime for both. Previously all files where just copied
over from the build system, generating random mtimes.

Signed-off-by: Paul Spooren <mail@aparcar.org>

target/imagebuilder/Makefile

@@ -86,7 +86,10 @@ endif
 	(cd $(PKG_BUILD_DIR); find staging_dir/host/bin/ $(IB_LDIR)/scripts/dtc/ -type f | \
 		$(XARGS) $(SCRIPT_DIR)/bundle-libraries.sh $(PKG_BUILD_DIR)/staging_dir/host)
 	STRIP=sstrip $(SCRIPT_DIR)/rstrip.sh $(PKG_BUILD_DIR)/staging_dir/host/bin/
-	$(TAR) -cf - -C $(BUILD_DIR) $(IB_NAME) | xz -T$(if $(filter 1,$(NPROC)),2,0) -zc -7e > $@
+	(cd $(BUILD_DIR); \
+		tar -I '$(STAGING_DIR_HOST)/bin/xz -7e -T$(if $(filter 1,$(NPROC)),2,0)' -cf $@ $(IB_NAME) \
+		--mtime="$(shell date --date=@$(SOURCE_DATE_EPOCH))"; \
+	)
 
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 prepare:

target/sdk/Makefile

@@ -152,7 +152,8 @@ $(BIN_DIR)/$(SDK_NAME).tar.xz: clean
 	find $(SDK_BUILD_DIR) -name CVS | $(XARGS) rm -rf
 	-make -C $(SDK_BUILD_DIR)/scripts/config clean
 	(cd $(BUILD_DIR); \
-		tar -I 'xz -7e' -cf $@ $(SDK_NAME); \
+		tar -I '$(STAGING_DIR_HOST)/bin/xz -7e -T$(if $(filter 1,$(NPROC)),2,0)' -cf $@ $(SDK_NAME) \
+		--mtime="$(shell date --date=@$(SOURCE_DATE_EPOCH))"; \
 	)
 
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