* cygtls.h (_cygtls::signal_debugger): Change argument type.
(_cygtls::copy_context): Delete declaration.
* exceptions.cc (exception::handle): Don't call copy_context() here.  Move
signal_handler call earlier and always call it.
(_cygtls::copy_context): Delete definition.
(_cygtls::signal_debugger): Move copy_context logic here.  Suspend thread
receiving signal before gathering context information.