Unbreak the build on FreeBSD 10.
Unbreak the build on FreeBSD 10.

isnan expands into a use of a function called _Generic.

Tell xform not to worry about it.

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket