convert shebang lines: python -> python3
diff --git a/Tools/scripts/ifdef.py b/Tools/scripts/ifdef.py
index 2ed7a66..46167ad 100755
--- a/Tools/scripts/ifdef.py
+++ b/Tools/scripts/ifdef.py
@@ -1,4 +1,4 @@
-#! /usr/bin/env python
+#! /usr/bin/env python3
 
 # Selectively preprocess #ifdef / #ifndef statements.
 # Usage: