[compiler-rt] Use SignalContext in ErrorStackOverflow and ErrorDeadlySignal

Summary: Part of https://github.com/google/sanitizers/issues/637

Reviewers: eugenis, alekseyshl, filcab

Subscribers: kubamracek, llvm-commits, dberris

Differential Revision: https://reviews.llvm.org/D37793

llvm-svn: 313168