cwrappers.go uses *C.void instead of unsafe.Pointer

[bcmills]

The Go equivalent to C's void* type is unsafe.Pointer, and the cgo tool automatically wraps functions that accept or return void* to accept or return unsafe.Pointer instead.

cwrappers.go currently includes some functions that accept *C.void arguments, but none of them are actually called. If they were, you would likely find that the call sites require two conversions (to unsafe.Pointer and then to *C.void) where they should need only one (to unsafe.Pointer).

[bcmills]

(See golang/go#21878.)