4.2.1 tarball from tddft.org is missing testsuite/CMakeLists.txt
The gitlab tag-provided tarball is fine, but the one linked to from Download (http://www.tddft.org/programs/octopus/down.php?file=libxc/4.2.1/libxc-4.2.1.tar.gz) (at least) misses testsuite/CMakeLists.txt.
I think testsuite/Makefile.am needs to be adjust to include it, likely via dist_noinst_DATA
.
I didn't check the earlier tarballs.