Ok, porting in a C library isn't that hard, i'm using Newlib in my kernel. Here is a tutorial to start: http://wiki.osdev.org/Porting_Newlib.
You basically need to:
- Compile the library (for example Newlib) using your cross compiler
- Provide stub-implementations for a list of system functions (like fork, fstat, etc.) in your kernel
- Link the library and your kernel together
If you want to use functions like malloc or printf (which uses malloc internally), you need some kind of memory management and simplest working implementation of sbrk.