[2020-02][runtime] Improve handling crashing signals (#19019)
* [runtime] Improve handling crashing signals
The default handlers for SIGTRAP, SIGSYS on macOS and Linux crash the process, so we now have Mono report this.
This patch also changes how the name of the signal is acquired for passing on to the crash reporting functions, allowing code reuse on crashing signals.
* [mono] Remove SIGTRAP handler, as it interferes with debugging
See https://github.com/mono/mono/pull/18243#issuecomment-
586013427
* Fix lack of cleanup for SIGSYS