Index: libstdc++-v3/config/os/bsd/darwin/os_defines.h
===================================================================
--- libstdc++-v3/config/os/bsd/darwin/os_defines.h.orig
+++ libstdc++-v3/config/os/bsd/darwin/os_defines.h
@@ -39,4 +39,9 @@
 // -flat_namespace to work around the way that it doesn't.
 #define _GLIBCXX_WEAK_DEFINITION __attribute__ ((weak))
 
+// Configure checks for nanosleep fail on Darwin, but nanosleep and
+// sched_yield are always available, so use them.
+#define _GLIBCXX_USE_NANOSLEEP 1
+#define _GLIBCXX_USE_SCHED_YIELD 1
+
 #endif