Avoid 'variable uninitialized when used within its own initialization' warning.
Initialize the static flyweight ex objects with the pointeed numeric
objects instead of using self-assignment. This is 100% equivalent to
before: The objects have already been initialized by the library_init
ctor so all the static object's ctor does is increment the pointeed
object's refcount.
According to the resolution of C++ core language defect 363 the warning is
incorrect because it is allowed to pass a reference to the object, see
<https://wg21.link/cwg363>. Incrementing the bp's refcount is okay too,
because the pointee numeric object has been fully initialized by the
library_init ctor. However, the compiler can hardly know this, so CLang++
issues a warning.