Use #ifdef for Explicit 32-bit Versus 64-bit Prototypes

In some cases, specific 32-bit and 64-bit versions of an interface are unavoidable. In the headers, these would be distinguishable by the use of the _LP64 or _ILP32 feature test macros. Similarly, code that is to work in 32-bit and 64-bit environments might also need to utilize the appropriate #ifdefs, depending on the compilation mode.