Make FAST_INT_BINDING strict again.

For [GHC ticket ~~#8102~~ #8022](http://ghc.haskell.org/trac/ghc/ticket/8022), the compiler bootstrap will fail using `happy-1.8.10` since it will now reject the invalid lifted pattern by default in the `stage2` build.

It would be nice to see this merged and `happy-1.8.11` released for developers. (It's always nice to get rid of old crufty warnings and whatnot.)