[llvm] OrcV2: also set COFF flag overrides when custom linking layer is used (PR #129533)

[Wenzel Jakob via llvm-commits]

wjakob wrote:

> Do you actually need to control where the JIT'd memory lives, or just its layout? I'm wondering if we could get by with a "SectionMerger" plugin that merges all blocks into a single section with RWX permissions, plus maybe a custom section-based memory manager if you need to control where it goes?

I don't need control over the absolute address, just having a single section will be enough. A `SectionMerger` plugin, if accessible through the C API, would be perfect (and likely much simpler than the current workaround with the memory manager).

https://github.com/llvm/llvm-project/pull/129533