runtime: fix 386, arm build
runtime: fix 386, arm build

CL 68150047 lost runtime.panicdivide.

TBR=dfc
CC=golang-codereviews
https://codereview.appspot.com/68610043

pombredanne/go-deleteme,tv42/old-go,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,tv42/old-go,pombredanne/go-deleteme,pombredanne/go-deleteme,tv42/old-go,tv42/old-go