O is for optimized: add the optimized flag for release builds

Author: phausler

lib/script.py

@@ -111,7 +111,7 @@ def generate_products(self):
         if Configuration.current.build_mode == Configuration.Debug:
             swift_flags += "-g -Onone "
         elif Configuration.current.build_mode == Configuration.Release:
-            swift_flags += " " 
+            swift_flags += "-O "
 
         swift_flags += Configuration.current.extra_swift_flags