Add test-powerpc to CI

With the example results file from #102, the test file [`SheepShaver/src/kpx_cpu/src/test/test-powerpc.cpp`](https://github.com/emaculation/macemu/blob/master/SheepShaver/src/kpx_cpu/src/test/test-powerpc.cpp) can somehow be leveraged to conduct automated tests.

It's unclear how this test should be built and executed, beyond the observations that:
1. the `ppc-testresults.dat` file (MD5 `3e29432abb6e21e625a2eef8cf2f0840`) should be stored in compressed form as `ppc-testresults.dat.bz2` (MD5 `60172863f951c72e1ee7e01d54ed6db3`) -- 36MB vs 4.6MB
2. the test file seems to want to be provided as an input argument to the test program
3. the test file is handled differently depending on architecture (and I haven't dug into it further)