libtoolize: Fix conflicting warnings about AC_PROG_RANLIB

libtoolize: Fix conflicting warnings about AC_PROG_RANLIB

The macro _LT_CMD_OLD_ARCHIVE inlines the definition of AC_PROG_RANLIB,
which seems to be outdated functionality. Running autoscan in a
directory with ltmain.sh produces conflicting warnings with libtoolize
about AC_PROG_RANLIB. Autoconf warns that AC_PROG_RANLIB is missing,
but libtoolize warns that it is obsolete. The outdated warning should
no longer appear after replacing AC_CHECK_TOOL(RANLIB, ranlib, :) with
AC_REQUIRE([AC_PROG_RANLIB]).

* m4/libtool.m4: Use AC_REQUIRE([AC_PROG_RANLIB]).
* Makefile.am: Added in tests/bug_42313.at.
* tests/bug_42313.at: Contains test cases for bug 42313.