Allow libc++ to be built on systems without POSIX threads

If you're crazy enough to want this sort of thing, then add
-D_LIBCPP_HAS_NO_THREADS to your CXXFLAGS and
--param=additiona_features=libcpp-has-no-threads to your lit commnad line.

http://reviews.llvm.org/D3969


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@217271 91177308-0d34-0410-b5e6-96231b3b80d8

src/memory.cpp

@@ -9,8 +9,10 @@
 
 #define _LIBCPP_BUILDING_MEMORY
 #include "memory"
+#ifndef _LIBCPP_HAS_NO_THREADS
 #include "mutex"
 #include "thread"
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -119,7 +121,7 @@ __shared_weak_count::__get_deleter(const type_info&) const _NOEXCEPT
 
 #endif  // _LIBCPP_NO_RTTI
 
-#if __has_feature(cxx_atomic)
+#if __has_feature(cxx_atomic) && !_LIBCPP_HAS_NO_THREADS
 
 static const std::size_t __sp_mut_count = 16;
 static pthread_mutex_t mut_back_imp[__sp_mut_count] =
@@ -172,7 +174,7 @@ __get_sp_mut(const void* p)
     return muts[hash<const void*>()(p) & (__sp_mut_count-1)];
 }
 
-#endif // __has_feature(cxx_atomic)
+#endif // __has_feature(cxx_atomic) && !_LIBCPP_HAS_NO_THREADS
 
 void
 declare_reachable(void*)