autoheader: warning: autoconf input should be named 'configure.ac', not 'configure.in'

[malaterre]

It seems recent autotools do not handle this anymore:

configure.in:850: the top level
configure.in:866: warning: The macro `AC_TRY_LINK' is obsolete.
configure.in:866: You should run autoupdate.
./lib/autoconf/general.m4:2920: AC_TRY_LINK is expanded from...
configure.in:866: the top level
autoheader: warning: autoconf input should be named 'configure.ac', not 'configure.in'

[malaterre]

I can get away with the following steps:

$ git mv configure.in configure.ac
$ sed -i -e 's/configure.in/configure.ac/g' Makefile

let me know if you prefer a Pull Request