Handle NeXT, POSIX, and setpgid in pp_sys.c and POSIX.
--- /dev/null
+# NeXT *does* have setpgid when we use the -posix flag, but
+# doesn't when we don't. The main perl sources are compiled
+# without -posix, so the hints/next_3.sh hint file tells Configure
+# that d_setpgid=undef.
+$self->{CCFLAGS} = $Config{ccflags} . ' -posix -DHAS_SETPGID' ;