Set up return type before flagging we're set up.
Set up return type before flagging we're set up.

Fixes a race condition when multiple threads use a native callsite
for the first time.

nbrown/rakudo,nbrown/rakudo,nbrown/rakudo,softmoth/rakudo,lucasbuchala/rakudo,samcv/rakudo,lucasbuchala/rakudo,rakudo/rakudo,jonathanstowe/rakudo,samcv/rakudo,labster/rakudo,softmoth/rakudo,rakudo/rakudo,samcv/rakudo,sjn/rakudo,raydiak/rakudo,tbrowder/rakudo,Gnouc/rakudo,nbrown/rakudo,samcv/rakudo,softmoth/rakudo,jonathanstowe/rakudo,rakudo/rakudo,tbrowder/rakudo,tbrowder/rakudo,MasterDuke17/rakudo,tbrowder/rakudo,tony-o/rakudo,lucasbuchala/rakudo,rakudo/rakudo,awwaiid/rakudo,Gnouc/rakudo,MasterDuke17/rakudo,Gnouc/rakudo,usev6/rakudo,tony-o/rakudo,lucasbuchala/rakudo,usev6/rakudo,labster/rakudo,sjn/rakudo,sjn/rakudo,tbrowder/rakudo,raydiak/rakudo,tony-o/rakudo,MasterDuke17/rakudo,labster/rakudo,awwaiid/rakudo,labster/rakudo,tony-o/rakudo,raydiak/rakudo,softmoth/rakudo,salortiz/rakudo,salortiz/rakudo,Gnouc/rakudo,labster/rakudo,lucasbuchala/rakudo,awwaiid/rakudo,nbrown/rakudo,sjn/rakudo,jonathanstowe/rakudo,tbrowder/rakudo,awwaiid/rakudo,Gnouc/rakudo,labster/rakudo,usev6/rakudo,MasterDuke17/rakudo,Gnouc/rakudo,MasterDuke17/rakudo,salortiz/rakudo,jonathanstowe/rakudo,salortiz/rakudo,salortiz/rakudo,awwaiid/rakudo,MasterDuke17/rakudo,rakudo/rakudo,salortiz/rakudo,samcv/rakudo,rakudo/rakudo,tony-o/rakudo,sjn/rakudo,raydiak/rakudo,usev6/rakudo,tony-o/rakudo,softmoth/rakudo,jonathanstowe/rakudo,nbrown/rakudo,usev6/rakudo