#869 Harmonize printing of pointers vs. uintptr_t

[Philipp Klaus Krause]

The C standard gives us lots of freedom for the %p format for the printf family.
IMO, we should use this freedom to always print pointers like we print hex uintptr_t.

Printing them like uintptr_t is reasonably easy on the users, and gives us a simpler, and smaller printf implementation.