[lld] [LLD] [COFF] Add a separate option for allowing duplicate weak symbols (PR #68077)

[Fangrui Song via llvm-commits]

MaskRay wrote:

> A test in compiler-rt/test/profile/Windows/coverage-weak-lld.cpp does currently enable the -lldmingw flag in an MSVC context, in order to deal with duplicate weak symbols.

I added the test in in 2021 when investigating Windows's weak symbols: https://maskray.me/blog/2021-04-25-weak-symbol#pecoff

I haven't added similar tests elsewhere. Thank you for making a standalone option. I wonder whether anyone has a channel to tell MSVC that this is a wanted feature by default.

https://github.com/llvm/llvm-project/pull/68077