sys/unix/*.c formatting and PANICTRACE fix

I started out just reformatting the function header for regularize()
but ended up doing miscellaneous other stuff, including some code
changes.  I think the CHDIR code is a bit cleaner now, but shouldn't
have any differences in behavior.

Along the way I noticed that 'nethack -dpath' or 'nethack -d path'
modifies argv[] before PANICTRACE attempted to save argv[0], so would
break having nethack invoke gdb to get a backtrace.  ('ARGV0' seems to
be unnecessary since 'hname' holds the same value, but I didn't get rid
of it....)

doc/fixes36.1

@@ -547,6 +547,8 @@ X11: color didn't work when the map was displayed as text rather than tiles
 X11: use grayscale monster tiles for statues
 X11/USE_XPM: [post-3.6.0 issue] the 'tiles' bug of incorrect total_tiles_used
 	for STATUES_LOOK_LIKE_MONSTERS broke XPM manipulation of tiles data
+PANICTRACE: PANICTRACE_GDB used wrong value for ARGV0 when launching gdb if
+	'nethack -dpath' was used to specify non-default playground directory
 
 
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