Update config/libtool.m4 to support ppc64le.

This version of config/libtool.m4 is from libtool 2.4.2.418,
downloaded and extracted from
ftp://alpha.gnu.org/gnu/libtool/libtool-2.4.2.418.tar.xz
per request from Deepak C Shetty <deepakcs@linux.vnet.ibm.com>
and ravi@linux.vnet.ibm.com.
Regenerate autotools files with new config/libtool.m4