Glib/GObject is pretty good and seems to be what you're looking for: https://developer.gnome.org/glib/2.37/ It's not tied to the GNOME platform at all but rather contains building blocks such as hash maps, linked and array lists, heap allocators, string manipulation functions and so on. Personally, I find some parts of GObject to be over engineered and distasteful but most of it is solid utility.
Then you have https://wiki.gnome.org/Vala which is a whole new language built on top of C + Glib/Object whose main selling point is that it compiles to, and is totally compatible with, plain C code.
Do keep in mind that all of this, Glib, Vala, Cello and other "make C more like a high-level language" are basically hacks to workaround the fact that C is a very low-level language and lacks many powerful features. I believe one is much more productive using Glib + C than just plain C, but you are still less productive than if you had choosen a modern language in the first place.
Then you have https://wiki.gnome.org/Vala which is a whole new language built on top of C + Glib/Object whose main selling point is that it compiles to, and is totally compatible with, plain C code.
Do keep in mind that all of this, Glib, Vala, Cello and other "make C more like a high-level language" are basically hacks to workaround the fact that C is a very low-level language and lacks many powerful features. I believe one is much more productive using Glib + C than just plain C, but you are still less productive than if you had choosen a modern language in the first place.