build: image: use UTC for zip timestamp

Zip uses DOS timestamp for mtime which is stored in local time and hence
depends on the timezone of the build system. Force zip to use UTC timezone
to make image builds more reproducible.

Signed-off-by: Sungbo Eo <[email protected]>

include/image-commands.mk

@@ -541,8 +541,7 @@ define Build/zip
 	rm -rf [email protected]
 	mkdir [email protected]
 	mv $@ [email protected]/$(word 1,$(1))
-
-	$(STAGING_DIR_HOST)/bin/zip -j -X \
+	TZ=UTC $(STAGING_DIR_HOST)/bin/zip -j -X \
 		$(if $(SOURCE_DATE_EPOCH),--mtime="$(SOURCE_DATE_EPOCH)") \
 		$(wordlist 2,$(words $(1)),$(1)) \
 		$@ [email protected]/$(if $(word 1,$(1)),$(word 1,$(1)),$$(basename $@))