rlog: ftbfs with autoconf 2.70

[Code7R]

This is a proxy ticket for http://bugs.debian.org/978897

The package fails to build in a test rebuild on at least amd64 with
autoconf 2.70, but succeeds to build with autoconf 2.69. The
severity of this report will be raised before the bookworm release,
so nothing has to be done for the bullseye release.

The full build log can be found at:
http://qa-logs.debian.net/2020/09/26.ac270/rlog_1.4-4_unstable_ac270.log

[Code7R]

Apart from that, can we just switch this to CMake and get rid of AC?

I could contribute a cmake setup if you want me to.