size assert not compatible with randomized struct layouts

[the8472]

rowan/src/green/node.rs

Lines 30 to 31 in 73ed5e7

	#[cfg(target_pointer_width = "64")]
	static_assert!(mem::size_of::<GreenChild>() == mem::size_of::<usize>() * 2);

breaks when compiling with layout randomization

If the assert is necessary for correctness then repr(C) should be used on the struct and its children to get deterministic layouts.
If it's just an optimization then it's probably better to just check it in tests/CI.

Found this while trying to build the rust compiler with randomized layouts. rust-lang/rust#101339