[FunctionAttrs] Failure to infer nounwind for function with nounwind inline asm

[nikic]

https://llvm.godbolt.org/z/GbhjKE6Ex

; RUN: opt -S -passes=function-attrs < %s
define void @test() {
  call void asm "", ""() nounwind
  ret void
}

For some reason nounwind does not get inferred, even though the inline asm call is nounwind.

[nikic]

Probably because of this HasUnknownCall check: https://github.com/llvm/llvm-project/blob/80c43b6c07f25792718dc2ee3490b9d817c65b1f/llvm/lib/Transforms/IPO/FunctionAttrs.cpp#L2288C14-L2288C28

We shouldn't be checking that as we can still do inference for unknown calls with call-site attributes. Need to check whether that causes any compile-time problems...