Renamed Py_Main to PyMac_Main as it has a different signature than the "normal" Py_Main, and that signature has appeared in a .h file.
diff --git a/Mac/Python/macmain.c b/Mac/Python/macmain.c
index c703cdc..9e5a300 100644
--- a/Mac/Python/macmain.c
+++ b/Mac/Python/macmain.c
@@ -86,7 +86,7 @@
 
 PyMac_PrefRecord PyMac_options;
 
-static void Py_Main(int, char **, char *); /* Forward */
+static void PyMac_Main(int, char **, char *); /* Forward */
 void PyMac_Exit(int); /* Forward */
 
 /* Initialize the Mac toolbox world */
@@ -537,7 +537,7 @@
 
 	}
 
-	Py_Main(argc, argv, script);
+	PyMac_Main(argc, argv, script);
     return 0;
 }
 
@@ -580,14 +580,14 @@
 			exit(0);
 		}
 	}
-	Py_Main(argc, argv, script);
+	PyMac_Main(argc, argv, script);
 }
 #endif /* TARGET_API_MAC_OSX */
 
 /* Main program */
 
 static void
-Py_Main(int argc, char **argv, char *filename)
+PyMac_Main(int argc, char **argv, char *filename)
 {
 	int sts;
 	char *command = NULL;