Fixes [YOCTO 5463]
Added the TUNE_ARCH variable. Also placed a cross-reference to
TUNE_ARCH in the TARGET_ARCH variable.
(From yocto-docs rev: 85d2a49323e0040b263b6d7f08fd036a25297b05)
Signed-off-by: Scott Rifenbark <scott.m.rifenbark@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>