Replace usleep call by nanosleep

Also improve behavior in case signals are delivered to the sleeping
thread. This fixes a potential security weakness reported by codacy
(interaction of usleep with SIGALRM and other timer functions such
as sleep(), alarm(), setitimer(), and nanosleep() is unspecified).

src/libCom/osi/os/posix/epicsAtomicOSD.cpp

@@ -48,8 +48,10 @@ void epicsAtomicLock ( EpicsAtomicLockKey * )
         status = pthread_mutex_lock ( & mutex );
         if ( status == 0 ) return;
         assert ( status == EINTR );
-        static const useconds_t retryDelayUSec = 100000;
-        usleep ( retryDelayUSec );
+        struct timespec retryDelay = { 0, 100000000 };
+        struct timespec remainingDelay;
+        while (nanosleep(&retryDelay, &remainingDelay) == -1 && errno == EINTR)
+            retryDelay = remainingDelay;
         countDown--;
         assert ( countDown );
     }