* libltdl/argz.h: Moved from here...

* libltdl/argz.h: Moved from here...
* libltdl/argz_.h: ...to here, so as not to shadow system
argz.h when we `#include <argz.h>' for example.
#include stdlib.h and sys/types.h to ensure we get a size_t
definition.
* libltdl/argz.c (HAVE_CONFIG_H): Set it up how ltdl likes it when
used by another client.
* m4/argz.m4: New file.
(gl_FUNC_ARGZ): Try to find an error_t definition, and a system
argz.h.
* m4/ltdl.m4: Use it.
(AC_LTDL_FUNC_ARGZ): Removed.
* libltdl/lt__glibc.h: #include <argz.h> to pick up either the
system argz.h or our libltdl/argz.h if necessary.
* libltdl/Makefile.am (libltdl_la_SOURCES): Move argz.h from
here...
(ltdldata_DATA): ...here. Along with argz.c.
(argz.h): Generate from argz_.h if the system file is missing.
Reported by Ralf Wildenhues <Ralf.Wildenhues@gmx.de>