Log Message:
math/py-scipy: fix build on NetBSD/powerpc (at least!)

In the unuran part, omit defining _ISOC99_SOURCE.  I am told that
the ieeefp.h header should not be used with _ISOC99_SOURCE.  (Its
use comes from pyport.h.)  Lately I've seen this package fail to
build also for aarch64, have not verified that this fixes it, though
it's not entirely impossible.

Fixes what triggered PR#56892.

Bump PKGREVISION.