Enable ptrace events on new child processes.

Enable ptrace events on new child processes.

New child processes on FreeBSD do not inherit optional ptrace events
such as fork and LWP events from the parent process.  Instead,
explicitly enable events on new children when reporting a fork
event.

gdb/ChangeLog:

	* fbsd-nat.c (fbsd_wait): Use "fbsd_enable_proc_events" on
	new child processes.