maybe optimize ++$i to $i = $i + 1 for native int
maybe optimize ++$i to $i = $i + 1 for native int

A conjectural optimization that maybe we won't need, so enabled at
$!level >= 4.  But if by xmas we don't get spesh to the point where
it optimizes this, we can just relax to $!level >= 3 and get the
optimization on native ints.

MasterDuke17/rakudo,lucasbuchala/rakudo,ugexe/rakudo,zostay/rakudo,labster/rakudo,samcv/rakudo,tony-o/rakudo,softmoth/rakudo,softmoth/rakudo,ungrim97/rakudo,raydiak/rakudo,Gnouc/rakudo,labster/rakudo,azawawi/rakudo,labster/rakudo,nbrown/rakudo,sjn/rakudo,salortiz/rakudo,LLFourn/rakudo,awwaiid/rakudo,labster/rakudo,zostay/rakudo,ugexe/rakudo,azawawi/rakudo,salortiz/rakudo,usev6/rakudo,ab5tract/rakudo,labster/rakudo,usev6/rakudo,rakudo/rakudo,tony-o/rakudo,Gnouc/rakudo,salortiz/rakudo,ungrim97/rakudo,paultcochrane/rakudo,salortiz/rakudo,nbrown/rakudo,salortiz/rakudo,usev6/rakudo,jonathanstowe/rakudo,labster/rakudo,awwaiid/rakudo,usev6/rakudo,LLFourn/rakudo,awwaiid/rakudo,b2gills/rakudo,lucasbuchala/rakudo,dankogai/rakudo,samcv/rakudo,azawawi/rakudo,tony-o/rakudo,softmoth/rakudo,softmoth/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,MasterDuke17/rakudo,b2gills/rakudo,tbrowder/rakudo,paultcochrane/rakudo,nbrown/rakudo,zostay/rakudo,dankogai/rakudo,samcv/rakudo,paultcochrane/rakudo,MasterDuke17/rakudo,Gnouc/rakudo,azawawi/rakudo,rakudo/rakudo,rakudo/rakudo,ab5tract/rakudo,samcv/rakudo,ugexe/rakudo,usev6/rakudo,sjn/rakudo,samcv/rakudo,zostay/rakudo,tbrowder/rakudo,nbrown/rakudo,lucasbuchala/rakudo,raydiak/rakudo,tbrowder/rakudo,LLFourn/rakudo,dankogai/rakudo,tony-o/rakudo,Gnouc/rakudo,jonathanstowe/rakudo,ab5tract/rakudo,dankogai/rakudo,nbrown/rakudo,ugexe/rakudo,jonathanstowe/rakudo,ungrim97/rakudo,softmoth/rakudo,sjn/rakudo,Gnouc/rakudo,dankogai/rakudo,tony-o/rakudo,LLFourn/rakudo,nbrown/rakudo,lucasbuchala/rakudo,jonathanstowe/rakudo,tbrowder/rakudo,rakudo/rakudo,ab5tract/rakudo,salortiz/rakudo,sjn/rakudo,raydiak/rakudo,awwaiid/rakudo,azawawi/rakudo,paultcochrane/rakudo,b2gills/rakudo,ungrim97/rakudo,sjn/rakudo,MasterDuke17/rakudo,raydiak/rakudo,rakudo/rakudo,rakudo/rakudo,LLFourn/rakudo,ugexe/rakudo,tbrowder/rakudo,lucasbuchala/rakudo,ungrim97/rakudo,paultcochrane/rakudo,jonathanstowe/rakudo,ab5tract/rakudo,Gnouc/rakudo,b2gills/rakudo,b2gills/rakudo,tony-o/rakudo,awwaiid/rakudo