opam > 2.1 changes the timestamp on source files

[mtelvers]

With reference to ocaml/opam-repository#28495. The package fails to build on opam > 2.1 as automake is not installed. This appears as a straightforward dependency problem, but automake is only required as the timestamp on the build files is not maintained.

As mentioned in the PR discussion, the extraction/copy behaviour changed in opam 2.2. Previously, the source tarball was extracted in place, whereas in opam >= 2.2 it is extracted into the source directory, then copied to the build directory. The copy does not retain the original time stamps, which results in make deciding that it needs to regenerate the configure script.

[kit-ty-kate]

Thanks for the report. I believe this should be fixed by #6440 but it's currently not in a ready state yet.