[dev.garbage] runtime: fix 32-bit build
[dev.garbage] runtime: fix 32-bit build

TBR=crawshaw
R=crawshaw
CC=golang-codereviews
https://codereview.appspot.com/168860046

webfd/go-zh,webfd/go-zh,d0f/go-zh,d0f/go-zh,webfd/go-zh,bryanxu/go-zh,bryanxu/go-zh,bryanxu/go-zh,d0f/go-zh,webfd/go-zh,webfd/go-zh,d0f/go-zh,d0f/go-zh,webfd/go-zh,webfd/go-zh,bryanxu/go-zh,d0f/go-zh,webfd/go-zh,bryanxu/go-zh,bryanxu/go-zh,d0f/go-zh,bryanxu/go-zh,bryanxu/go-zh,d0f/go-zh