Avoid 'variable uninitialized when used within its own initialization' warning.

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.