Loading CustomXCTestRunner framework two times is not possible

[stanislaw]

Loading the CustomXCTestRunner framework two times, each from a different test, results in llvm-jit-objc getting confused about where or not CustomXC* classes have to be registered manually or not:

JIT Error: Objective-C class is already registered: CustomXCTestObserver
registerOneClass: CustomXCTestObserver 
	source ptr: 0x000000010d43ba18
0x000000010D43BA18

The implementation must understand that some classes are registered by dyld so they must be skipped from loading by llvm-jit-objc.