This fixes compilation of the ath9k-htc firmware. Before that, loading
it would result in "Target is unresponsive". The patches come from
the ath9k-htc firmware source.
* gnu/packages/patches/ath9k-htc-firmware-binutils.patch,
gnu/packages/patches/ath9k-htc-firmware-gcc.patch: New files.
* gnu-system.am (dist_patch_DATA): Add them.
* gnu/packages/cross-base.scm (package-with-patch): New procedure.
(cross-binutils): Check whether TARGET starts with "xtensa-", and call
'package-with-patch' when it does.
(cross-gcc-patches): New procedure.
(cross-gcc): Use it to add patches.
