Release tarballs requiring automake to build

[alerque]

For some reason the v0.15.x release tarballs to date are requiring automake on the target system to build. This should not be necessary as the necessary scripts should be pre-generated. Building from Git requires GNU Autotools, but the source tarball should not.

This first cropped up building for Homebrew (see Homebrew/homebrew-core#175586) but I've confirmed it in an Arch Linux Docker image.

The most likely culprit that comes to mind is the aminclude.am system being used to reuse boilerplate with simple includes. Maybe something in there is triggering the configure script to touch something that makes Make think it needs to rebuild.