[v3] RFC make check-abi, round 2

[Benjamin Kosnik]

> @test_lib@ was unexpanded in generated Makefile (since it is possible
> that I didn't regen automake targets properly, perhaps ignore this for now)

Caught this after I posted the patch last night. It's fixed in my tree.

Since there seems to be consensus, I'll check this in.

Thanks y'all.

It looks like you and Phil both have work to put in, and I'd like it if
you could put in the baselines for BSD, that would be cool.

-benjamin