MacOs detection is broken #402
Description
The current code wrongly detects CPU_FEATURES_OS_MACOS and CPU_FEATURES_OS_IPHONE.
The documentation states that TARGET_OS_OSX and TARGET_OS_IPHONE are always defined and set to 0 or 1.
So we should test for the value instead of the presence.
As of today, both CPU_FEATURES_OS_MACOS and CPU_FEATURES_OS_IPHONE are always defined when targeting an Apple device.