progs, libs: support _RANLIB overrides

progs, libs: support _RANLIB overrides

Much like we have per-target support for _AR and _LINK, add an _RANLIB
override too.  This allows selection of specific ranlib tools in case
a non-standard archiver tool was forced.

* bin/automake.in: Check for _RANLIB per-target settings.
* doc/automake.texi: Document _RANLIB override.
* lib/am/library.am: Change $(RANLIB) to $(%XLIBRARY%_RANLIB).
* t/list-of-tests.mk: Add ranlib_override.sh.
* t/ranlib_override.sh: New test.
* NEWS: Mention new feature.