Add libunwind switch, this makes it have a chance to compile
codes which are conditioned by "HAVE_LIBUNWIND_H"
Signed-off-by: Wenlin Kang <wenlin.kang@windriver.com>
Signed-off-by: Yi Zhao <yi.zhao@windriver.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>