C ABI: Add C support for passing structs of floats to an extern function

[FireFox317]

Currently this does not handle returning these structs yet, because I'm not sure where in the Zig codebase this is handled.

Also while working on this, I found out that the code that detects which C ABI Class should be used is quite outdated (from 2014). Version 1.0 can be found here (Yes, official documents on a github wiki page lol).

Also, this looks like a bug. Its iterating but then only looking at the first field, same issue for the union case. Basically this code needs a refactor.

zig/src/analyze.cpp

Lines 7978 to 7979 in 2ae9e06

	for (uint32_t i = 0; i < ty->data.structure.src_field_count; i += 1) {
	X64CABIClass field_class = type_c_abi_x86_64_class(g, ty->data.structure.fields[0]->type_entry);

Related: #1481

[andrewrk]

Nice work!

[andrewrk]

Did this solve #3211 ?

[daurnimator]

Did this solve #3211 ?

No, that issue is about returning structs; this PR adds passing structs (as arguments).