Makefile: set TZ LANG LC_ALL

To be reproducible, TZ LANG LC_ALL should be set early
in the build process to be always used.

Change-Id: Iad802968347c8d41f974af930e0d0ad5b66719cb
Signed-off-by: Alexander Couzens <lynxis@fe80.eu>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35391
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@gmail.com>

Makefile

@@ -42,6 +42,12 @@ absobj := $(abspath $(obj))
 COREBOOT_EXPORTS := COREBOOT_EXPORTS
 COREBOOT_EXPORTS += top src srck obj objutil objk
 
+# reproducible builds
+LANG:=C
+LC_ALL:=C
+TZ:=UTC0
+COREBOOT_EXPORTS += LANG LC_ALL TZ
+
 DOTCONFIG ?= $(top)/.config
 KCONFIG_CONFIG = $(DOTCONFIG)
 KCONFIG_AUTOADS := $(obj)/cb-config.ads