This is still some cleanup, and does not fix much wrt step / continue,
but it introduces dbg_thread_set_single_step that is going to be useful
for individual thread control and let us remove all remaining uses of
gdbctx->context.
Signed-off-by: Rémi Bernon <rbernon@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>