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Summary:
When referencing NSURLSessionTaskPriorityDefault (e.g.) on iOS 8 with optimizations enabled, the runtime crashes:

dyld: Symbol not found: _NSURLSessionTaskPriorityDefault
  Referenced from: /Users/zacharywest/Library/Developer/CoreSimulator/Devices/4DA14D1B-48B0-49BC-9DE6-965F412E4CC9/data/Containers/Bundle/Application/936B5CCC-9688-4AF7-B59D-6A7751132DC1/NSURLSessionTaskCrash.app/NSURLSessionTaskCrash
  Expected in: /Library/Developer/CoreSimulator/Profiles/Runtimes/iOS 8.4.simruntime/Contents/Resources/RuntimeRoot/System/Library/Frameworks/Foundation.framework/Foundation
 in /Users/zacharywest/Library/Developer/CoreSimulator/Devices/4DA14D1B-48B0-49BC-9DE6-965F412E4CC9/data/Containers/Bundle/Application/936B5CCC-9688-4AF7-B59D-6A7751132DC1/NSURLSessionTaskCrash.app/NSURLSessionTaskCrash


When running without optimizations enabled, this does not crash. This header is flagged:

FOUNDATION_EXPORT const float NSURLSessionTaskPriorityDefault NS_AVAILABLE(10_10, 8_0);
FOUNDATION_EXPORT const float NSURLSessionTaskPriorityLow NS_AVAILABLE(10_10, 8_0);
FOUNDATION_EXPORT const float NSURLSessionTaskPriorityHigh NS_AVAILABLE(10_10, 8_0);

It should be accessible anywhere 8.0 and above. It is not, with optimizations.

Steps to Reproduce:
1. Reference NSURLSessionTaskPriorityDefault on iOS 8
2. Run with optimizations enabled
3. Crash

Expected Results:
The float is available.

Actual Results:
The float crashes.

Version:
Xcode 7.2 & Xcode 7.1 both have this behavior

Notes:
Attached is a sample project. It's literally:

1. File > New Project
2. Deployment target 8.0
3. Add a reference to NSURLSessionTaskPriorityDefault
4. Run as 'release' in the simulator.

No kidding. Seriously, that's it. Happens every time.

Happens _on the App Store_.

Configuration:
iOS 8.x

Attachments:
'NSURLSessionTaskCrash.zip' was successfully uploaded.