build system: use a single variable name for compiler runtimes

We build with either gcc or clang, no need to keep both around

Change-Id: I9af2cc7636bdc791a68ba8ed6e7c5a81973c5dfd
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/7552
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
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>