While gdb can figure it out, libunwind requires CFI directives to
unwind a leaf function, even though the directives are trivial.
Adding them matches what GCC outputs, and likely gdb has many
heuristics that less complex tools (e.g. profilers) may not.
Bug: 181
Change-Id: I25c72152de33109a29710a828aeb99c608dd0470
Reviewed-on: https://boringssl-review.googlesource.com/c/33964
Commit-Queue: David Benjamin <davidben@google.com>
Reviewed-by: Adam Langley <agl@google.com>