xcompile: Add a way to specify -march=i586

Instead of instructing users to edit xcompile when they want to build
a quark platform, give the build a way to set -march=586 so that
the quark code will build correctly.  The Quark processor does not
support the instructions introduced with the Pentium 6 architecture.

Change-Id: I0ed69aadc515f86f76800180e0e33bcd75feac5a
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/13552
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Tested-by: build bot (Jenkins)
Reviewed-by: Leroy P Leahy <leroy.p.leahy@intel.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: FEI WANG <wangfei.jimei@gmail.com>
2 files changed