Includes don't control linking, and traditional C did not require function prototypes, so most compilers (in non-C++ mode at least) will happily compile calls to unknown functions, it just assumes a default signature.

I know that and mach_* are supposed to be dynamically loaded. But what I failed to get is to reproduce the kernel panic, not to build and run on my iPhone 5. By now that piece of code could run but only result in normal crash, not kernel panic.