Turn on whole module optimization for Swift in Release configuration. (#17)

Configurations/Project/Release.xcconfig

@@ -17,7 +17,7 @@ VALIDATE_PRODUCT = YES
 
 // Optimization
 GCC_OPTIMIZATION_LEVEL = s
-SWIFT_OPTIMIZATION_LEVEL = -O
+SWIFT_OPTIMIZATION_LEVEL = -Owholemodule
 
 // Preprocessor
 ENABLE_NS_ASSERTIONS = NO