nv50/ir: wrap assertion using typeid in #ifndef NDEBUG

Note: this is a candidate for the 9.0 stable branch.

src/gallium/drivers/nv50/codegen/nv50_ir.cpp

@@ -715,7 +715,9 @@ Instruction::clone(ClonePolicy<Function>& pol, Instruction *i) const
 {
    if (!i)
       i = new_Instruction(pol.context(), op, dType);
+#ifndef NDEBUG // non-conformant assert, so this is required
    assert(typeid(*i) == typeid(*this));
+#endif
 
    pol.set<Instruction>(this, i);