xcompile: Use GCC wrappers for ar, nm

xcompile: Use GCC wrappers for ar, nm

When compiling with GCC, use the special wrappers around ar and nm that
provide the path to the plugin they need to understand LTO object files.
These wrappers forward all other functionality to the underlying
programs, so they should otherwise be equivalent.

Change-Id: Ibdae4faabf67bf6a4bb8c38970f6189646ee74b3
Signed-off-by: Jacob Garber <jgarber1@ualberta.ca>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38290
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>