Add support for the structure of function-like macros.

We accept the structure of arguments in both macro definition and
macro invocation, but we don't yet expand those arguments. This is
just enough code to pass the recently-added tests, but does not yet
provide any sort of useful function-like macro.

glcpp.h

@@ -52,9 +52,15 @@ glcpp_parser_parse (glcpp_parser_t *parser);
 void
 glcpp_parser_destroy (glcpp_parser_t *parser);
 
-int
-glcpp_parser_macro_defined (glcpp_parser_t *parser,
-			    const char *identifier);
+typedef enum {
+	MACRO_TYPE_UNDEFINED,
+	MACRO_TYPE_OBJECT,
+	MACRO_TYPE_FUNCTION
+} macro_type_t;
+
+macro_type_t
+glcpp_parser_macro_type (glcpp_parser_t *parser,
+			 const char *identifier);
 
 /* Generated by glcpp-lex.l to glcpp-lex.c */