GDB's 'target extended-remote' and 'set detach-on-fork' are related,
but neither the same nor orthogonal. Better use two bools.

Task-number: QTCREATORBUG-17264
Task-number: QTCREATORBUG-16978
Change-Id: I50dfcdf8f69fadcc6dff2dcf632e4bdfe28a28bf
Reviewed-by: Vikas Pachdha <vikas.pachdha@qt.io>
Reviewed-by: hjk <hjk@qt.io>