Use signed encoding when using relative CFI addresses.

This is required for gdb to work.
libunwind works with either encoding.

(cherry picked from commit 17065880693d1b15ffeb60b9955a2d092839977f)

Bug: 21924613
Change-Id: I4e4f1cf9c65d48fa885a5993eeeed0253a3f2579
1 file changed