v.gen.c: fix cgen regression after f457b94 (prevented vinix builds), add tests

vlib/v/gen/c/fn.v

@@ -1310,8 +1310,16 @@ fn (mut g Gen) ref_or_deref_arg(arg ast.CallArg, expected_type ast.Type, lang as
 				if arg.expr.is_lvalue() {
 					g.write('(voidptr)&/*qq*/')
 				} else {
-					needs_closing = true
-					g.write('ADDR(${g.typ(expected_deref_type)}/*qq*/, ')
+					mut atype := expected_deref_type
+					if atype.has_flag(.generic) {
+						atype = g.unwrap_generic(atype)
+					}
+					if atype.has_flag(.generic) {
+						g.write('(voidptr)&/*qq*/')
+					} else {
+						needs_closing = true
+						g.write('ADDR(${g.typ(atype)}/*qq*/, ')
+					}
 				}
 			}
 		}

vlib/v/tests/generics_indirect_test.v

@@ -0,0 +1,32 @@
+const zzz = &Local{}
+
+struct Local {
+	aborted bool
+}
+
+pub fn current() &Local {
+	return zzz
+}
+
+pub fn store<T>(var &T, value T) {
+	eprintln('store ${voidptr(var)} <- $value')
+	unsafe {
+		*var = value
+	}
+}
+
+fn test_generic_over_a_local_boolean_address() {
+	eprintln('-'.repeat(40))
+	mut mybool := false
+	println(mybool)
+	store(mybool, true)
+	println(mybool)
+	eprintln('-'.repeat(40))
+}
+
+fn test_generic_over_a_const_returned_by_a_fn() {
+	println(current().aborted)
+	store(current().aborted, true)
+	println(current().aborted)
+	eprintln('-'.repeat(40))
+}