Remove our special-casing of zero-length `memcpy`/`memset` for WebAssembly with LLVM 20

[alexrp]

zig/src/codegen/llvm.zig

Lines 10065 to 10071 in aa7d138

	// Any WebAssembly runtime will trap when the destination pointer is out-of-bounds, regardless
	// of the length. This means we need to emit a check where we skip the memset when the length
	// is 0 as we allow for undefined pointers in 0-sized slices.
	// This logic can be removed once https://github.com/ziglang/zig/issues/16360 is done.
	const intrinsic_len0_traps = o.target.isWasm() and
	ptr_ty.isSlice(zcu) and
	std.Target.wasm.featureSetHas(o.target.cpu.features, .bulk_memory);

llvm/llvm-project#112617

[Luukdegram]

#16360 can be closed as well as it was the original tracking issue.

[alexrp]

Ah, I hadn't seen that one. Let's just use that then.