Utils: Don't use ptrace in the process stub

Previously, ptrace was used to keep a tight hold on the spawned process
across the exec(), followed by raising a SIGSTOP to allow un-racy
attaching a debugger.

This makes implementation of 'Run as root' more difficult and is
apparently not needed: instead of the ptrace use, the SIGSTOP can be
raised directly, before exec().

Change-Id: I36025ac547b2a335e2a203c728d221830e4c0a7d
Reviewed-by: Christian Stenger <christian.stenger@qt.io>
Reviewed-by: Christian Kandeler <christian.kandeler@qt.io>

src/plugins/debugger/gdb/gdbengine.cpp

@@ -1157,7 +1157,8 @@ void GdbEngine::handleStopResponse(const GdbMi &data)
         const QString func = frame["func"].data();
         if (from.endsWith("/ld-linux.so.2")
                 || from.endsWith("/ld-linux-x86-64.so.2")
-                || func == "clone")
+                || func == "clone"
+                || func == "kill")
         {
             showMessage("INTERNAL CONTINUE AFTER SIGSTOP FROM STUB", LogMisc);
             notifyInferiorSpontaneousStop();