MINOR: tools: add generic pointer hashing functions

MINOR: tools: add generic pointer hashing functions

There are a few places where it's convenient to hash a pointer to compute
a statistics bucket. Here we're basically reusing the hash that was used
by memory profiling with a minor update that the multiplier was corrected
to be prime and stand by its promise to have equal numbers of 1 and 0,
and that 32-bit platforms won't lose range anymore.

A two-pointer variant was also added.