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 <fe@dev.tdt.de>
Link: https://github.com/openwrt/openwrt/pull/15987
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>