build system: Split linking into multiple steps

After collecting dependencies for ramstage, add an intermediate step
in which object files are linked per directory. The results are then
linked into the final binary.

This reduces the maximum command line length and might also help with
future use of LTO linking.

Also adapt the lint test for build dir handling, since printall
doesn't provide individual object files for ramstage anymore.

Change-Id: Ie40febd8c1eaf4609944eedeab46d870639e53df
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/1911
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
2 files changed