std.Target: Fix cTypePreferredAlignment() to always return 1 for avr.

[alexrp]

This matches avr-gcc's ABI.

Note that this makes us diverge from Clang 19's AVR ABI. But we already did that in other ways for AVR, so I don't consider that a significant issue. (Right now, we're in a weird middle-ground where we don't fully match Clang or avr-gcc.) I'm working on getting Clang to match avr-gcc as well, which should hopefully make it into Clang 20.

Also worth noting:

zig/src/Type.zig

Lines 1639 to 1641 in d5c9d85

	pub fn maxIntAlignment(target: std.Target, use_llvm: bool) u16 {
	return switch (target.cpu.arch) {
	.avr => 1,