POSIX semaphores use CLOCK_REALTIME, but our semaphore_t abstraction
expects CLOCK_MONOTONIC based times. Use the mutex/condvar based
fallback if time_monotonic() actuall returns monotonic times.
#include <library.h>
+#if defined(HAVE_CLOCK_GETTIME) && \
+ (defined(HAVE_CONDATTR_CLOCK_MONOTONIC) || \
+ defined(HAVE_PTHREAD_COND_TIMEDWAIT_MONOTONIC))
+/* if we use MONOTONIC times, we can't use POSIX_SEMAPHORES since they use
+ * times based on CLOCK_REALTIME */
+#undef HAVE_SEM_TIMEDWAIT
+#endif /* HAVE_CLOCK_GETTIME && ... */
+
#ifdef HAVE_SEM_TIMEDWAIT
#include <semaphore.h>
#else /* !HAVE_SEM_TIMEDWAIT */