Implement remaining LCG functions

Implements the remaining functions for LCG random number generation (erand48(), nrand48(), jrand48(), seed48() and lcong48()).

These functions expect either a size-3 or size-7 array as input arguments, which is implemented using pointer parameters (the only way I could get it to work without incorrect behavior or compiler warnings). The default XI has been changed from a u64 to a [c_ushort; 3] for consistency with the rest of the code, even though it leads to a bit more raw pointer handling.

Output is verified as identical to that from glibc.