fix(const_eval): break from checking const type after walking to function pointer

Author: EvanMerlock

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -356,6 +356,7 @@ impl<'mir, 'tcx> Checker<'mir, 'tcx> {
             };
 
             match *ty.kind() {
+                ty::FnPtr(_) => break,
                 ty::Ref(_, _, hir::Mutability::Mut) => self.check_op(ops::ty::MutRef(kind)),
                 _ => {}
             }