Fix Joubert's complaint that int8-sized numeric literals are mishandled

on Alpha (because parser mistakenly assumes that a nonoverflow result
from strtol means the value will fit into int4).  A scan for other uses
of strtol and strtoul found a couple other places with the same mistake;
fix them too.  The changes are all conditional on HAVE_LONG_INT_64 to
avoid complaints from compilers that think x != x is a silly test
(cf. pg_atoi).