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

[via llvm-commits]

aokblast wrote:

Emm, the objcopy works fine when writing small code with lit test. The problem is discovered inside our company's inner codebase and the binary is about 5kb. I don't know if the size matter because it is a samba mount in Linux (Client) to Windows (Server).

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