If targeting only Linux workloads, use something like checkinstall to generate all lib-xyz-dev flavours.
If targeting cross platform, settle on one of conan, vcpkg or cmake packages.
A "classic C library" cannot assume the existence of pkg-config (or checkinstall, or conan, or vcpkg, or cmake).
It can assume the existence of the preprocessor.
EDIT: Since you modified the comment, it can at very least assume the existence of a compiler, a linker and make.
The OP library has a design such that the only build system you need is the preprocessor. That is a perfectly valid design decision, especially since this is explicitly for lighter-weight uses where GLib would be excessive. If you don't like it, don't use it.
EDIT: Clang, for example, does not provide a `make` or guarantee a `make` exists. It will happily co-exist with BSD make on FreeBSD, or GNU make on macOS, or no make at all. I assume you concede on pkg-config, etc.
Another example of lack of understanding how C toolchains work.
Since the days C got outside Bell Labs, every single C compiler has provided those tools.
Ignoring 50 years of C practices in library distribution is exactly that, willful ignorance.