build: allow obj=/absolute/path

This allows moving the build tree outside the source tree.

Change-Id: I97882c4820d2c962c27bf8d50378e64016ce5790
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/5803
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
1 file changed