debuggerd_handler: receive abort messages via sigqueue(DEBUGGER_SIGNAL).

Make it possible for code such as fdsan that generates debugging
tombstones via raise(DEBUGGER_SIGNAL) to pass an abort message as well.

Bug: http://b/112770187
Test: debuggerd_test
Change-Id: Idc34263241c18033573e466da3a45aa6f716ddb3
1 file changed