Inefficient codegen in builder pattern with existed copyable base value

[CrazyboyQCD]

First found in #128081 (comment)

In a builder pattern code, when building with existed copyable base value, codegen isn't efficient like partial copy.
This can be reproduced on both argument value and constant value.

Full copy and patial copy:
C version: https://godbolt.org/z/z3fWsKhqE
Rust version: https://godbolt.org/z/MeGf8E5Gd

Existed value and non existed value:
C version: https://godbolt.org/z/9z3x3Kv5c
Rust version: https://godbolt.org/z/vWEaEfd3e

Real use case examaple in rust: https://godbolt.org/z/3q9jn5c1o

[apiraino]

WG-prioritization assigning priority (Zulip discussion).

@rustbot label -I-prioritize +P-medium

[CrazyboyQCD]

Close this in favor of llvm/llvm-project#113134

[dianqk]

We’d better keep it open until a test case for the fix is added to Rust.