Auto merge of #111634 - marc0246:arc-new-uninit-bloat, r=thomcc

Fix duplicate `arcinner_layout_for_value_layout` calls when using the uninit `Arc` constructors

What this fixes is the duplicate calls to `arcinner_layout_for_value_layout` seen here: https://godbolt.org/z/jr5Gxozhj

The issue was discovered alongside #111603 but is otherwise unrelated to the duplicate `alloca`s, which remain unsolved. Everything I tried to solve said main issue has failed.

As for the duplicate layout calculations, I also tried slapping `#[inline]` and `#[inline(always)]` on everything in sight but the only thing that worked in the end is to dedup the calls by hand.

Author: bors