Patch merged into coreboot/master: buildgcc: Use smaller xz archives

the following patch was just integrated into master:
commit d9d2102bec67f07c29870aea4cbebe2492bae2c4
Author: Stefan Reinauer 
Date:   Thu Apr 21 18:16:30 2016 -0700

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 
    Reviewed-on: https://review.coreboot.org/14462
    Reviewed-by: Timothy Pearson 
    Tested-by: build bot (Jenkins)
    Reviewed-by: Paul Menzel

See https://review.coreboot.org/14462 for details.

-gerrit