Compile pgenmain.c and printgrammar.c with PGEN defined
diff --git a/Parser/pgenmain.c b/Parser/pgenmain.c
index 88fa7f1..4b7b55a 100644
--- a/Parser/pgenmain.c
+++ b/Parser/pgenmain.c
@@ -13,6 +13,8 @@
    - check for duplicate definitions of names (instead of fatal err)
 */
 
+#define PGEN
+
 #include "Python.h"
 #include "pgenheaders.h"
 #include "grammar.h"