[lld] [lld][COFF]Expose UnifiedLTO and PassPipeline Options (PR #69904)

[Reid Kleckner via llvm-commits]

rnk wrote:

Sorry I missed this question
> I'm not sure how to convert my cpp reproducible to an LTO test case. Kinda need some help on that part.
I guess I would look at the ELF test case and try to remodel it for COFF: 
https://github.com/llvm/llvm-project/commit/ab9b3c84a588f86e7f66eeb577bea7155817ff06#diff-71ce44d5f2d7691e5ce7dd5907ddec5a2a8092b1743d8d65ad33a92fece521a1

https://github.com/llvm/llvm-project/pull/69904