If you need just linked list, I would suggest to implement it yourself. Depending on functionality you need it can be very small amount of code - 10/20 lines or so.
As for ready-to-use C code for data structures:
- here's OpenBSD queue.h and tree.h that implements various queues (singly/doubly linked lists/arrays) and tree structures
- klib good implementation for various data structures
- TommyDS with various stuff
- libldfs if you need lock-free data structures
- stb.h - also has some data structures
You can also take a look at some implementations of memory allocators to see what they use:
- tlsf - implements linked list within its data structure, not as external wrapper
- Hoard
- nedmalloc
- ltalloc - C++ not C, but does not use STL