How to consume C (static) library from SwiftUI application in Xcode Version 15.4 (15F31d)?

Imagine you have nice C static library which source code (especially files and directories structure) you shouldn't change. Library's public headers are full of double-quoted includes.

How would you call a function, defined in such a library, from SwiftUI application?

Example project shown on screenshot contains C++ library because initially I looked for Swift/C++ interoperability, but since virtual functions are not yet available in Swift, my question now is about old plain vanilla C.

My deployment target for now is macOS only, if this matters.