improve the C backend lowering of Zig types to C types

[andrewrk]

There are two functions where we lower Zig types to C types:

zig/src/codegen/c.zig

Lines 727 to 733 in 83a4bb6

	fn renderTypeAndName(
	dg: *DeclGen,
	w: anytype,
	ty: Type,
	name: CValue,
	mutability: Mutability,
	) error{ OutOfMemory, AnalysisFail }!void {

zig/src/codegen/c.zig

Line 471 in 83a4bb6

fn renderType(dg: *DeclGen, w: anytype, t: Type) error{ OutOfMemory, AnalysisFail }!void {

Right now it is hacky and not correct for more complex types. It needs to be improved to fully support C types, particularly regarding function pointers.

Thankfully, @Vexu already solved this problem in arocc so we can borrow from this project:

https://github.com/Vexu/arocc/blob/361274f0e4b5a4b1f1cab029077ac968914fa255/src/Type.zig#L1285

Part of this issue is coming up with complex Zig types as test cases and making sure they properly lower to C types.