Implement simplified substitution for function-like macro invocation.

This supports function-like macro invocation but without any argument
substitution. This now makes test 11 through 14 pass.
diff --git a/glcpp.h b/glcpp.h
index bd599d7..043098b 100644
--- a/glcpp.h
+++ b/glcpp.h
@@ -51,6 +51,7 @@
 {
 	int ival;
 	char *str;
+	string_list_t *string_list;
 	token_t *token;
 	token_list_t *token_list;
 } YYSTYPE;