Fix return type of % operator.

See https://github.com/dherman/asm.js/issues/69 and
https://bugzilla.mozilla.org/show_bug.cgi?id=878433#c9
asm-llvm: Disallow 1e-1 as an integer literal (but allow 1e-0, 1e3, etc).

See https://github.com/dherman/asm.js/issues/57