configure: Use LT_INIT from libtool 2 instead of deprecated AC_PROG_LIBTOOL
AC_PROG_LIBTOOL
was replaced by LT_INIT
in libtool 2 in 2008,
so it's time to rely on it.
Clears autoconf warnings:
configure.ac:40: warning: The macro 'AC_PROG_LIBTOOL' is obsolete.
configure.ac:40: You should run autoupdate.
m4/libtool.m4:100: AC_PROG_LIBTOOL is expanded from...
configure.ac:40: the top level