Add the non-negative-fixnum to the cross-compiler support code.
Add the non-negative-fixnum to the cross-compiler support code.

Needed for build. I'll have to introduce a cross-typep at some point...

rvedam/Mezzano,varjagg/Mezzano,froggey/Mezzano,AugustusHuang/Mezzano,rvedam/Mezzano,froggey/Mezzano,AugustusHuang/Mezzano,varjagg/Mezzano