generate argz.c and argz.in.h from glibc sources

generate argz.c and argz.in.h from glibc sources

* config/argz.mk: New file, with rules to generate the two files.
* modules/argz (Depends-on): Add mempcpy, stpcpy, strndup
and strnlen.  Suggested by David Lutterkort.
* m4/argz.m4: Require AC_C_RESTRICT.
Check only for the existence of one function,
argz_replace, since it seems to have been added most recently.
Also, remove the side effect of defining HAVE_ARGZ_* symbols.
* lib/argz.c: Now generated directly from glibc sources, rather than
imported from libtool.  Includes the following additional functions:
argz_extract, argz_create, argz_delete, str_append, argz_replace.
* lib/argz.in.h: Likewise.
* config/srclist.txt: Reflect that argz* files are no longer pulled
from libtool.