Implement @align in C backend

[Gankra]

kdl-script supports an align attribute, which the rust backend implements. The C backend should implement it too (currently it bails if it finds any attributes at all, pending implementations like this one). Currently the C backend contains a commented-out version of the rust impl, so you can roughly see what should be done:

abi-cafe/src/abis/c/declare.rs

Lines 345 to 356 in 6ba6865

	"c doesn't support attrs yet".to_owned(),
	))?;
	}
	/*
	let mut default_c_repr = true;
	let mut repr_attrs = vec![];
	let mut other_attrs = vec![];
	for attr in attrs {
	match attr {
	Attr::Align(AttrAligned { align }) => {
	repr_attrs.push(format!("align({})", align.val));

The main issue is picking the attribute to use, perhaps by checking what compiler we're using. I know there's like, way too many different attributes here. Someone with more C experience than me hopefully has Opinions on which to use where.

[Gankra]

https://en.cppreference.com/w/c/language/_Alignas