Request change of ptrace scope from KCrash

Summary:

• On Linux recent kernels only allow attaching a debugger to a process if
  • the right to attach to processes is enabled system-wide
  • the debugger is an ancestor of the debuggee
  • or the debuggee sets a tracer process by a call to prctl(PR_SET_PTRACER, debugger_pid, 0, 0, 0);
• DrKonqi will ask the debuggee by a socket connection to set a new ptracer. This is required if an external debugger is started (using the usually hidden Debug button).
• When the debugger has finished, the access is requested back to DrKonqi to allow internal backtraces again.

Test Plan:

• try to attach gdb or KDevelop to the process by using the Debug button: operation will not be permitted
• apply corresponding patches to KCrash D11236 and DrKonqi
• the process can now be debugged
• after detaching the debugger again, a backtrace can be created using the DrKonqi dialog as usual

Reviewers: Plasma: Workspaces, Frameworks, ossi

Reviewed By: ossi

Subscribers: ossi, lepagevalleeemmanuel, maximilianocuria, adridg, plasma-devel

Tags: Plasma

Differential Revision: https://phabricator.kde.org/D11235