[lld] [LLD][COFF] Create COFFObjectFile instance when constructing ObjFile (NFC) (PR #120144)

[Alexandre Ganea via llvm-commits]

aganea wrote:

How does this do in terms of link time when linking large monolithic/static binaries? Are you able to profile? I am thinking about PEs that bring in lots of libraries during link, ie. clang.exe linked with /MT, chrome.exe in non-component mode or Unreal Engine Editor in monolithic mode. The change seems ok, but better be sure.

https://github.com/llvm/llvm-project/pull/120144