Self-hosted linkers are very endian-dirty

[alexrp]

The ELF and Mach-O linkers are riddled with endian bugs; grepping for asBytes, @ptrCast, or writeAll will turn up most of them. Also, SPIR-V:

zig/src/link/SpirV.zig

Lines 288 to 290 in 73f863a

	// TODO endianness bug. use file writer and call writeSliceEndian instead
	linker.base.file.?.writeAll(@ptrCast(linked_module)) catch |err|
	return diags.fail("failed to write: {s}", .{@errorName(err)});