Add workflow for ppc64 (#348)

[Oppen]

[lemire]

It seems that we are still getting failures with this architecture.

[lemire]

--- FAIL: TestLargeFile (0.00s)
    bsi64_test.go:266: 
        	Error Trace:	bsi64_test.go:266
        	Error:      	Expected nil, but got: &os.PathError{Op:"open", Path:"./testdata/age/EBM", Err:0x2}
        	Test:       	TestLargeFile

[lemire]

@Oppen Do you know what the error is about?

[Oppen]

Yes, I stalled work on this for now, but the issue is that it doesn't know how to find the input when I build the tests in a separate step (I currently cross-compile the tests and later run them on the emulated machine). I suspect cding would be enough, but haven't tried yet.

I left it for a while, I think it may be a good idea to use the same PR for the other pipelines I thought of adding.