win32/build.py: add option --32

Author: MaxKellermann

win32/build.py

@@ -11,6 +11,8 @@
     arg = configure_args[0]
     if arg == '--64':
         x64 = True
+    elif arg == '--32':
+        x64 = False
     else:
         break
     configure_args.pop(0)