CU_ASSERT_PTR_NOT_NULL() not usable with function pointers in strict ANSI C

Originally reported as https://sourceforge.net/p/cunit/bugs/69/

Environment: gcc -ansi -Wpedantic -Werror

The CUnit macros for pointers, such as CU_ASSERT_PTR_NOT_NULL(), cannot be used with function pointers, because their definition casts the pointer arguments to void *.

In strict, warning-free ANSI C (gcc -ansi -Wpedantic -Werror), a function pointer may not be cast to an object pointer, and the GNU compiler will reject any program which attempts to do so.

Removing the cast to void * means that the code compiles without warnings.