glib on darwin: disable warnings to avoid prototype errors

vcunat did some reformatting before pushing.
Update readline for patch5 (needed for darwin13).
gawk: add gawkInteractive with readline support

stdenv (on linux) depends on gawk, readline and similar are useless for non-interactive usage.
Close #1596. Original patch was almost completely rewritten by vcunat.

On darwin we always specify whether to use readline, so it isn't always picked as reported.