illumos gate

another openbsd compatibility functions:

     The recallocarray() function is similar to reallocarray() except it
     ensures newly allocated memory is cleared similar to calloc().  If ptr is
     NULL, oldnmemb is ignored and the call is equivalent to calloc().  If ptr
     is not NULL, oldnmemb must be a value such that oldnmemb * size is the
     size of the earlier allocation that returned ptr, otherwise the behaviour
     is undefined.

     The freezero() function is similar to the free() function except it
     ensures memory is explicitly discarded.  If ptr is NULL, no action
     occurs.  If ptr is not NULL, the size argument must be equal or smaller
     than the size of the earlier allocation that returned ptr.  freezero()
     guarantees the memory range starting at ptr with length size is discarded
     while deallocating the whole object originally allocated.