RustWrapper: adapt for llvm/llvm-project@a38152e2156

[durin42]

I am only partially confident this is reasonable, and the argument is ignored on targets other than ARM64EC which appears to be some Windows 11 thing, and therefore I have no way to test.

@rustbot label: +llvm-main

[rustbot]

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[cuviper]

@wesleywiser perhaps you (or someone you know) could evaluate this Windows change?

[cjacek]

Non-hybrid targets should not use it to pass exports to writeImportLibrary, please use something like std::nullopt instead. I created llvm/llvm-project#81600 to clarify that.

[durin42]

Done, thanks!

[durin42]

The argument is now optional, so this shouldn't be needed. I'll open a new PR if we end up needing a change here.