Minor fix-ups for Darwin PowerPC

[barracuda156]

@ViralBShah This took forever :) Sorry for a ridiculous delay, it was forgotten.

Here are two tiny fixes:

1. Use a macro which includes ppc64, so that it is not left broken on macOS. (BTW, this still leaves out AIX, I believe?)
2. Make sure __BYTE_ORDER__ is actually defined: AFAIK, it may not be the case with some old gcc versions, and those support C99, so it is relevant.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 39.02%. Comparing base (4b83beb) to head (af8e580). Report is 3 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #303 +/- ## ========================================== + Coverage 38.24% 39.02% +0.78% ========================================== Files 233 233 Lines 6139 6144 +5 Branches 1607 1608 +1 ========================================== + Hits 2348 2398 +50 + Misses 3394 3393 -1 + Partials 397 353 -44 ```

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[ViralBShah]

Windows is trying to use gcc instead of clang. Otherwise, happy to merge.

[barracuda156]

@ViralBShah Thanks for merging! This was super-fast.

[ViralBShah]

Would you like me to tag a new release?

[barracuda156]

Would you like me to tag a new release?

That would be certainly helpful, thank you.

[ViralBShah]

Released 0.8.3

[barracuda156]

Released 0.8.3

Updated in MacPorts in https://github.com/macports/macports-ports/commit/9e4787078b3f00708932da4214d9642c3e458302