Install a signal handler for SIGABRT and SIGSEGV for kwin_wayland

Summary:
kwin_wayland disables ptrace on itself. This has the side effect of
core dumps no longer be created - which we want as DrKonqi doesn't
work for kwin_wayland.

This change introduces a dedicated signal handler for abort and
segfault. The signal handler enables ptrace again, unsets itself as
signal handler and raises the signal again, so that the proper crash,
abort handling can be performed.

Test Plan:
Added a crash, added an abort and verified that coredumpctl
shows the expected coredump.

Reviewers: Plasma on Wayland, KWin, bshah

Subscribers: plasma-devel, kwin

Tags: Plasma on Wayland, KWin

Differential Revision: https://phabricator.kde.org/D2003