Patch merged into coreboot/master: xcompile: use $() instead of backticks

the following patch was just integrated into master:
commit 033abe5e690d2533b768eae9c236bde70d514980
Author: Martin Roth 
Date:   Tue Jan 5 15:44:02 2016 -0700

xcompile: use $() instead of backticks

While the backtick syntax isn't actually deprecated, the $() syntax
    is preferred.  Since both styles were being used in this script, settle
    on the new standard for all cases.

Change-Id: I33770d666781b4fa34c909411e0d220c2540dbb4
    Signed-off-by: Martin Roth 
    Reviewed-on: https://review.coreboot.org/12843
    Tested-by: build bot (Jenkins)
    Reviewed-by: Patrick Georgi

See https://review.coreboot.org/12843 for details.

-gerrit