libcxx: Settle for bizarre inclusion scheme of libc++

Author: lhmouse

mcfgthread/libcxx.h

@@ -11,9 +11,6 @@
 #include "fwd.h"
 #include "gthr_aux.h"
 #include <errno.h>
-#if __MCF_CXX11(1+)0
-#  include <chrono>
-#endif
 
 #ifdef _LIBCPP_BEGIN_NAMESPACE_STD
 _LIBCPP_BEGIN_NAMESPACE_STD
@@ -347,14 +344,14 @@ __MCF_LIBCXX_IMPORT
 void
 __MCF_libcxx_thread_sleep_for_ns_count(int64_t __ns) __MCF_noexcept;
 
-#if __MCF_CXX11(1+)0
+#ifdef _LIBCPP___CHRONO_DURATION_H
 __MCF_ALWAYS_INLINE
 void
-__libcpp_thread_sleep_for(const ::std::chrono::nanoseconds& __ns) __MCF_noexcept
+__libcpp_thread_sleep_for(const chrono::nanoseconds& __ns) __MCF_noexcept
   {
     __MCF_libcxx_thread_sleep_for_ns_count(__ns.count());
   }
-#endif  /* C++11 */
+#endif  /* <chrono> included  */
 
 /* Gives up the current time slice, like `sched_yield()`.  */
 __MCF_LIBCXX_IMPORT