The header only libraries that I am familiar with always have a specific macro that needs to be defined so that the implementation part gets included, something like LIBRARYNAME_IMPLEMENTATION, otherwise they only define the header/declaration part, but not the implementation.
I think having something like that makes those libraries easier to use with Zig, because then you can do exactly what @LucasSantos91 described, only use translate-c/cImport on the header part.
Here is how raylib uses that to add raygui raylib/build.zig at 0dc4ba53dcc6ed2605c792647a33d58b12c23ee3 · raysan5/raylib · GitHub