Thank you very much for this report,
The 'libgnuastro_make.so' is declared within the
'debian/libgnuastro18.install' file (see [1] below); a comment there
also described what it is (an extension-library for GNU Make, described
in [2]).
Could you please point me to any other place that it should be declared?
This is an important bug and I will fix it as soon as I know the solution.
Thank you very much,
Mohammad
[1]
https://sources.debian.org/src/gnuastro/0.20-1/debian/libgnuastro18.install
[2] https://www.gnu.org/software/make/manual/html_node/Loading-Objects.html