stage2 can't load elements from arrays in structs

[Vexu]

test {
    const Entry = packed struct {
        unique_partition_guid: [2]u64,
    };
    var foo: Entry = .{ .unique_partition_guid = .{ 0, 0 }};
    // if ((&foo.unique_partition_guid).*[0] != 0) unreachable; // works
    if (foo.unique_partition_guid[0] != 0) unreachable; // assertion failure
}

thread 18003 panic: reached unreachable code
/home/vexu/Documents/zig/zig/lib/std/debug.zig:281:14: 0x6d0268 in std.debug.assert (zig)
    if (!ok) unreachable; // assertion failure
             ^
/home/vexu/Documents/zig/zig/src/codegen/llvm.zig:5178:19: 0xf2d641 in codegen.llvm.FuncGen.airStructFieldVal (zig)
            assert(!isByRef(field_ty));
                  ^
/home/vexu/Documents/zig/zig/src/codegen/llvm.zig:4162:64: 0xeffb14 in codegen.llvm.FuncGen.genBody (zig)
                .struct_field_val => try self.airStructFieldVal(inst),
                                                               ^

Could be related to #12215 since both are caused by the way array access is handled.

[Vexu]

Arrays are no longer allowed in packed structs.