build system: remove duplicate architecture list

Let xcompile pass the list of architectures, given
that it already has it.

Change-Id: I565512d3bef987c9a4e48a39bfd88bacf0b65de9
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/6254
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Marc Jones <marc.jones@se-eng.com>
2 files changed