Region: define static const functions returning infinite and empty regions

As per https://gcc.gnu.org/ml/gcc-help/2010-10/msg00255.html we can't define some
static variables as extern and link them statically inside objects.
Otherwise these might be redefined multiple times, allocated mutiple times and
destroyed, again, multiple times causing memory errors. (LP: #1749957, #1750619)

Approved by: Andrea Azzarone