Extend CI to cover 32bit, ARM and integer-gmp

[dcoutts]

We'd ideally like to extend CI to cover configurations:

• A 32bit build, either x86 or ARM
• An ARM platform
• GHC using integer-simple rather than integer-gmp
• Windows

We can only really ensure issues like #193 do not come back if we have CI covering them.

[GreenReaper]

Not sure if useful, but Debian's x32 ABI port has 32-bit pointers and triggered #193. It's otherwise 64-bit, and uses the x86_64 kernel, which might help if it could be on the same machine as x86_64.

[thoughtpolice]

For the record, Windows was working previously with AppVeyor, and it was our 32-bit build, and it did flush out issues as noted. That said my AppVeyor setup broke a while back and I haven't fixed it.

I think we should investigate moving to GitHub Actions for these CI workflows, honestly. Not only is the integration far better, but we can provision a quick ARM machine from some vendor like Scaleway perhaps and use that with a self-hosted runner, hooked up to GitHub.

[juhp]

Just noting for the record that on Fedora i686:

      *** Failed! Exception: 'toFlatTerm: encodePreEncoded used with invalid CBOR: DeserialiseFailure 0 "expected tag"' (after 46 tests and 46 shrinks):
      [(TTagged 4294967296 (TStringI ""),True)]
      Use --quickcheck-replay=6625 to reproduce.
1 out of 262 tests failed (1.24s)
Test suite tests: FAIL
Test suite logged to: dist/test/cborg-0.2.2.1-tests.log