Get rid of long datatype in CATCACHE_STATS enabled builds

Get rid of long datatype in CATCACHE_STATS enabled builds

"long" is 32 bits on Windows 64-bit.  Switch to a datatype that's 64-bit
on all platforms.  While we're there, use an unsigned type as these
fields count things that have occurred, of which it's not possible to
have negative numbers of.

Author: David Rowley <dgrowleyml@gmail.com>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Discussion: https://postgr.es/m/CAApHDvoGFjSA3aNyVQ3ivbyc4ST=CC5L-_VjEUQ92HbE2Cxovg@mail.gmail.com