Fix imports of builtin library.
Fix imports of builtin library.

diku-dk/futhark,ihc/futhark,diku-dk/futhark,HIPERFIT/futhark,ihc/futhark,diku-dk/futhark,HIPERFIT/futhark,ihc/futhark,diku-dk/futhark,HIPERFIT/futhark,diku-dk/futhark