system.create doesn't work with bitfield objects

[exelotl]

What happened?

in Nim 1.7.x you can no longer use system.create to allocate an object that uses the bitsize pragma.

Example

type Foo = object
  x {.bitsize:4.}: uint
  y {.bitsize:4.}: uint

let a = create(Foo)

Current Output

main.nim(5, 15) template/generic instantiation of `create` from here
system/memalloc.nim(148, 18) Error: 'sizeof' requires '.importc' types to be '.completeStruct'

Additional Information

This works fine in Nim 1.6 and older.

The error is related to #19040 , but only recently has it started triggering for system.create. I don't understand why the compiler would be trying to evaluate sizeof at compile time in this scenario, if it wasn't doing so before.

Nim Version

Nim Compiler Version 1.7.3 [Linux: amd64]
Compiled at 2022-10-07
Copyright (c) 2006-2022 by Andreas Rumpf

git hash: 0d23419e681c4ce561ec43dc4a66a0ed40b8009e
active boot switches: -d:release

[ringabout]

related 2bda4a3

[Araq]

No need to do anything but what we do in 1.6.