According to the linpac-0.21 README:
Release packages can be identified by the presence of the ./configure in
this directory. If the ./configure script is not present, then see the
'Hacking' instructions below.
The instructions are:
NOTES FOR HACKING
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A clean checkout from the GIT source repository is not ready to configure
and compile. You will need the GNU autotools
(https://en.wikipedia.org/wiki/GNU_build_system) to create the
./configure script and Makfile templates. Once the autotools are
installed the full build procedure is:
autoreconf --install
./configure
make
make install
So it seems you need to run autoreconf --install rather than plain autoconf. Alternatively, you could consider using linpac-0.20 instead, which appears to be the most up-to-date release version.