WIP: Merge upstream v3.3 into meson rewrite

Upstream finally fixed many (most? all?) of the same bugs, and released v3.3. I figure it's better to use the upstream fixes where it doesn't matter, to avoid future maintenance woes.

I'd also like them to switch to meson :). If this repo matches what they do more closely, it's an easier sell.

To that end, I've done a tentative merge of upstream into this meson rewrite. I just fixed comments, not sure on the best way to port over libffi's testsuite.

Lastly, in adding back those Windows 32-bit files, is this branch fixing a broken implementation or restoring a removed feature? I couldn't tell from the original upstream commit message what the intent was. I figure it would be good to know before giving upstream a PR.