base-files: add SOURCE_DATE_EPOCH as OPENWRT_BUILD_DATE to os-release

This commit adds the build date during compilation to the os-release file.
This information can then be used later to output this via the the ubus,

Signed-off-by: Florian Eckert <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/15987
Signed-off-by: Hauke Mehrtens <[email protected]>

include/version.mk

@@ -104,5 +104,6 @@ VERSION_SED_SCRIPT:=$(SED) 's,%U,$(call sed_escape,$(VERSION_REPO)),g' \
 	-e 's,%u,$(call sed_escape,$(VERSION_HOME_URL)),g' \
 	-e 's,%s,$(call sed_escape,$(VERSION_SUPPORT_URL)),g' \
 	-e 's,%P,$(call sed_escape,$(VERSION_PRODUCT)),g' \
-	-e 's,%h,$(call sed_escape,$(VERSION_HWREV)),g'
+	-e 's,%h,$(call sed_escape,$(VERSION_HWREV)),g' \
+	-e 's,%B,$(call sed_escape,$(SOURCE_DATE_EPOCH)),g'
 

package/base-files/files/usr/lib/os-release

@@ -16,3 +16,4 @@ OPENWRT_DEVICE_MANUFACTURER_URL="%m"
 OPENWRT_DEVICE_PRODUCT="%P"
 OPENWRT_DEVICE_REVISION="%h"
 OPENWRT_RELEASE="%D %V %C"
+OPENWRT_BUILD_DATE="%B"