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

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

@MaskRay This relates to the use of `-lldmingw` in compiler-rt/test/profile/Windows/coverage-weak-lld.cpp (in MSVC mode); I’d like to add this new flag and move that test over to using that flag. Because I would like to change `-lldmingw` so that it doesn’t add MSVC lib directories automatically, see https://reviews.llvm.org/D144084. Do you know if that flag is used in that way in MSVC environments anywhere else outside of that one test?

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