buildgcc: Use smaller xz archives

The xz archives are slightly smaller than the bz2 archives for gmp
and mpfr, so use them instead to speed up the download.

Change-Id: I3729455cdbc46e5a0cff119ecca97b0e00c3d402
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: https://review.coreboot.org/14462
Reviewed-by: Timothy Pearson <tpearson@raptorengineeringinc.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

0 files changed, 0 insertions, 0 deletions