Added code for generating nonnull attributes

src/codegen.cpp

@@ -2905,6 +2905,10 @@ static void do_code_gen(CodeGen *g) {
             if (param_type->id == TypeTableEntryIdPointer) {
                 // when https://github.com/andrewrk/zig/issues/82 is fixed, add
                 // non null attribute here
+
+                ///`i` is arg index + 1
+                ///I think that 0 is the return index, but it has a named LLVM constant variable
+                LLVMZigAddNonNullAttr(fn_table_entry->fn_value, param_decl_i + 1);
             }
             if (is_byval) {
                 // TODO