define YYSTYPE_IS_DECLARED to work with bison 2.3

parse.y

@@ -35,6 +35,8 @@
 
 #include "calmwm.h"
 
+#define YYSTYPE_IS_DECLARED
+
 TAILQ_HEAD(files, file)		 files = TAILQ_HEAD_INITIALIZER(files);
 static struct file {
 	TAILQ_ENTRY(file)	 entry;