[lld] [lld] lld/ELF/Writer.cpp: write directly to outs when output is "-" (PR #72061)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay requested changes to this pull request.

`ld.lld a.o -o -` already writes to stdout. See https://reviews.llvm.org/D56940

https://github.com/llvm/llvm-project/pull/72061