[llvm] [llvm-objcopy] fix llvm-objcopy replaced failed when the file is modified inplace (PR #121564)

[Fangrui Song via llvm-commits]

MaskRay wrote:

The title or body should mention archive.

Suggested title: `[llvm-objcopy] Fix in-place modification or archive when ...`

https://github.com/llvm/llvm-project/pull/121564