runtime: fix arm build (B not JMP)
runtime: fix arm build (B not JMP)

TBR=dvyukov
CC=golang-codereviews
https://codereview.appspot.com/71060046

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