cgen: fix printing fn call of returning c struct value

vlib/v/gen/c/str.v

@@ -118,7 +118,8 @@ fn (mut g Gen) gen_expr_to_string(expr ast.Expr, etype ast.Type) {
 		is_dump_expr := expr is ast.DumpExpr
 		is_var_mut := expr.is_auto_deref_var()
 		str_fn_name := g.get_str_fn(exp_typ)
-		temp_var_needed := expr is ast.CallExpr && expr.return_type.is_ptr()
+		temp_var_needed := expr is ast.CallExpr
+			&& (expr.return_type.is_ptr() || g.table.final_sym(expr.return_type).is_c_struct())
 		mut tmp_var := ''
 		if temp_var_needed {
 			tmp_var = g.new_tmp_var()

vlib/v/tests/c_structs/csize.h

@@ -0,0 +1,4 @@
+struct Size {
+   int width;
+	int height;
+};

vlib/v/tests/c_structs/return_csize_test.v

@@ -0,0 +1,15 @@
+#include "@VMODROOT/csize.h"
+
+struct C.Size {
+	width  int
+	height int
+}
+
+fn get_size() C.Size {
+	return C.Size{11, 22}
+}
+
+fn test_return_csize() {
+	println(get_size())
+	assert true
+}