Add a new debug knob for the FreeBSD native target.
    
    For now this just logs information about the state of the current LWP
    for each STOPPED event in fbsd_wait().
    
    gdb/ChangeLog:
    
    	* NEWS (Changes since GDB 8.1): Add "set/show debug fbsd-nat".
    	* fbsd-nat.c (debug_fbsd_nat): New variable.
    	(show_fbsd_nat_debug): New function.
    	(fbsd_wait): Log LWP info if "debug_fbsd_nat" is enabled.
    	(_initialize_fbsd_nat): Add "fbsd-nat" debug boolean command.
    
    gdb/doc/ChangeLog:
    
    	* gdb.texinfo (Debugging Output): Document "set/show debug
    	fbsd-nat".