disable external compression

It's not necessary, and determining the path of gzip/compress is annoying. If
we get it wrong, the NetHack thread starts spinning at 100% CPU constantly.

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
system.h: use strict prototyping for system functions

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
src/do_name.c: don't return temporary buffer

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
Makefile.top: use proper subdirectory make directives

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
eliminate format-security warnings

Signed-off-by: Steven Noonan <steven@uplinklabs.net>
unix/Makefiles: harden warning flags

Signed-off-by: Steven Noonan <steven@uplinklabs.net>