Just checking the docs at this stage so please forgive me if this is already done.
I haven't used autotools in ages and looking at your samples brings back bad memories

Have you considered adding support for pkg-config and, eventually, cmake?
Registering with pkg-config will help a lot as it will simplify integrating CopperSpice in other projects, regardless of that project using plain Makefile, Makefile.am or CMakeLists.
Having a recipe for cmake that has custom CopperSpice stuff would also be great, though pkg-config integration would make this less important - cmake already has support for pkg-config and it can get the required info from it.
I haven't built a program with autotools on Windows, but when I was doing that it was taking ages because of how they were constantly spawning new process, something that was very slow on Windows. Comparatively, at that time (4-5 years ago, I admit), building the same project with cmake was taking 25% or less of the time, just because of the way the final Makefile was created.
Cheers,
Ioan Calin