transpile: Rework is_va_list for better accuracy

[Rua]

• Fixes va_start type mismatch #1353.

This reworks the implementation of is_va_list, so that it is more accurate (less false positives/negatives). It's split into two subfunctions, one that detects va_list based on the __builtin_va_list typedef, and the other that detects based on the architecture-specific struct definition. Both methods have situations in which they don't work, so they are used together.

This has been confirmed to work on:

• Linux x86-64
• Linux x86-32 (was previously broken)

MacOS aarch64 is still failing if I enable it, because things like va_start seem to be unimplemented. Testing for Linux aarch64 will depend on #1283.

[kkysen]

Can you add the example from #1353 as a snapshot test? You can do that as a commit after the fixes, as prior to the fix, it wouldn't compile (if I'm understanding that correctly). Thanks!

[Rua]

It was only broken for x86-32, which the tests wouldn't catch anyway. Also since the same thing was suggested in #1443 (review) I'll go with that one instead.

[kkysen]

It was only broken for x86-32, which the tests wouldn't catch anyway. Also since the same thing was suggested in #1443 (review) I'll go with that one instead.

Ah, sounds good to me.