bpo-22831: Use "with" to avoid possible fd leaks in tools (part 2). (GH-10927)

diff --git a/Tools/scripts/ifdef.py b/Tools/scripts/ifdef.py
index b1711ce..22249b2 100755
--- a/Tools/scripts/ifdef.py
+++ b/Tools/scripts/ifdef.py
@@ -45,9 +45,8 @@
         if filename == '-':
             process(sys.stdin, sys.stdout)
         else:
-            f = open(filename, 'r')
-            process(f, sys.stdout)
-            f.close()
+            with open(filename) as f:
+                process(f, sys.stdout)
 
 def process(fpi, fpo):
     keywords = ('if', 'ifdef', 'ifndef', 'else', 'endif')