Add libunwind package dependency to solve following error:
configure: error: failed to find libunwind-ptrace.h
(From OE-Core rev: 50985a40021c20c8620e82b431ff2da8e005845d)
Signed-off-by: Chong Lu <Chong.Lu@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>