Raise SIGTRAP rather than abort on failure.

If gdb is attached, it's convenient to be able to continue running.

Change-Id: I3bbb2634d05a08f6bad5425f71da2210dbb80cfe
Reviewed-on: https://boringssl-review.googlesource.com/5125
Reviewed-by: Adam Langley <agl@google.com>
2 files changed