Fix segfault on "multi cross{}"
Fix segfault on "multi cross{}"

The builtin sub cross is an alias for infix X.  But we were assigning
instead of binding, so the aliasing was not complete.  This apparently
caused a segfault whenever someone wanted to have their own "cross".

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