[PATCH] [libc++] Allow libc++ to be built on systems without POSIX threads

[Jon Roelofs]

================
Comment at: include/memory:615
@@ -614,3 +614,3 @@
 #  include <atomic>
 #endif
 
----------------
I missed a pair of changes in this file. The __has_feature(cxx_atomic) #ifdef block needs to be:


```
#if __has_feature(cxx_atomic) && !defined(_LIBCXX_HAS_NO_THREADS)
...
#endif  // __has_feature(cxx_atomic) && !defined(_LIBCXX_HAS_NO_THREADS)
```

I also missed a pair of these in include/ios near lines 216 and 367

http://reviews.llvm.org/D3969