Fix the crashing on 64-bit systems
Fix the crashing on 64-bit systems

"multiply -1 -9223372036854775808" raises an arithmetic exception at
"anum / num". It doesn't crash on 32-bit systems because gcc uses a
function __divi3 to do the division instead of the CPU division
instruction directly.

giuliolunati/ren-c,draegtun/ren-c,mbk/ren-c,draegtun/ren-c,hostilefork/rebol,rebolsource/r3,giuliolunati/ren-c,rebolsource/r3,mbk/ren-c,earl/r3,codebybrett/ren-c,codebybrett/ren-c,draegtun/ren-c,kealist/ren-c,earl/r3,codebybrett/ren-c,kealist/ren-c,hostilefork/rebol,rebolsource/r3,codebybrett/ren-c,codebybrett/ren-c,kealist/ren-c,kealist/ren-c,hostilefork/rebol,giuliolunati/ren-c,mbk/ren-c,kealist/ren-c,rgchris/ren-c,rgchris/ren-c,draegtun/ren-c,rgchris/ren-c,earl/r3,rgchris/ren-c,rgchris/ren-c,hostilefork/rebol,codebybrett/ren-c,hostilefork/rebol,kealist/ren-c,draegtun/ren-c,giuliolunati/ren-c,draegtun/ren-c,earl/r3,hostilefork/rebol,giuliolunati/ren-c,mbk/ren-c