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

[Wenzel Jakob via llvm-commits]

wjakob wrote:

> Out of interest, do you know how much JIT'd code you usually load?

Not a huge amount (less than 1 GB). It's spread out into many small functions, and other much larger allocations happen in between. This is probably the cause.

> I think that we can expose enough for the callback above, if that's the right shape? (The full API is big, and still a moving target -- it'll be a while before JITLink has a fully featured C API)

In my case I don't think I really need to interact with JITLink besides turning it on (if not already on by default on Windows) and persisting/loading `.so` files representing individual compiled functions to a cache. The API surface is small (https://github.com/mitsuba-renderer/drjit-core/commit/8c5ec998eaeb10c4eaae9890a3a4a7c782d7b9ed).

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