build system: unify linker use across gcc and clang

Let's just call ld directly for gcc, too.

Change-Id: I305eb92ed0d21b098134a7eb5a9f9fe3b126aeea
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/7553
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
4 files changed