GenericTemplate.hs: workaround GHC 7.6 type checking failure
GenericTemplate.hs: workaround GHC 7.6 type checking failure

Even with an exact type signature for unbox_int and indexShortOffAddr
GHC 7.6 fails to realize the type for the second parameter of
indexShortOffAddr which needs to be of unboxed kind '#' instead
of boxed '*'.

    Couldn't match kind `#' against `*'
    In the second argument of `indexShortOffAddr', namely
      `(unbox_int $ bit `div` 16)'

It's probably due to `div`. Figured out we can use unboxed right
shift instead, to get it straight.

Tested with GHC 7.6.3, GHC 7.8.4, and GHC 7.10.3.

Signed-off-by: Dan Aloni <2591e5f46f28d303f9dc027d475a5c60d8dea17a@kernelim.com>

PhilThomas/happy,da-x/happy