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

[Marshall Clow]

I would also like to understand more about the motivation behind this patch.
Concurrency is a core part of C++11library, and just disabling it seems wrong to me.

I know there are systems w/o POSIX threads, but to support those systems, libc++ should use whatever primitives exist there, rather than just disabling all the threading support.

What are you trying to accomplish here?

http://reviews.llvm.org/D3969