Você precisa instalar o libtool, que fornece as macros necessárias. No Ubuntu,
apt-get install libtool
Eu baixei o libopus do git e tentei criá-lo, mas eu entendo,
Updating build configuration files, please wait....
configure.ac:38: warning: macro 'AM_PROG_LIBTOOL' not found in library
configure.ac:38: error: possibly undefined macro: AM_PROG_LIBTOOL
If this token and others are legitimate, please use m4_pattern_allow.
See the Autoconf documentation.
autoreconf: /usr/bin/autoconf failed with exit status: 1
Como resolvo esse erro?