strtoimax: Work around AIX 5.1 bug.

strtoimax: Work around AIX 5.1 bug.

* lib/inttypes.in.h (strtoimax): Allow overriding the system's
definition.
* m4/strtoimax.m4 (gl_FUNC_STRTOIMAX): Check against the AIX 5.1 bug.
Set HAVE_STRTOIMAX.
* m4/inttypes.m4 (gl_INTTYPES_H_DEFAULTS): Initialize
REPLACE_STRTOIMAX.
* modules/inttypes-incomplete (Makefile.am): Substitute
REPLACE_STRTOIMAX.
* modules/strtoimax (Files): Add m4/stdint_h.m4, m4/inttypes_h.m4.
(configure.ac): Test HAVE_STRTOIMAX, REPLACE_STRTOIMAX.
(Depends-on): Update conditions.
* tests/test-strtoimax.c (main): Add tests for large values.
* doc/posix-functions/strtoimax.texi: Mention the AIX 5.1 bug.