You can put those reimplentations in a different file. You don't have to expose the consumer of the library to them by jamming the whole thing, both interface and implementation, in a single header.

This is like library design by the folks who mistakenly say that what they do with '#include <stdio.h>' is they are "including a library". Eg. Compile and link are the same thing in a lot of people's minds, I think increasingly these days as C expertise is diminishing.