Reapply "[LockFileManager] Reduce default timeout time"

This reverts commit 9957204,
effectively reapplying 314651a
unchanged, now that the Clang commits it depends on are back in.

rdar://problem/30165583
rdar://problem/30171097

Author: dexonsmith

lib/Support/LockFileManager.cpp

@@ -290,9 +290,9 @@ LockFileManager::WaitForUnlockResult LockFileManager::waitForUnlock() {
   Interval.tv_sec = 0;
   Interval.tv_nsec = 1000000;
 #endif
-  // Don't wait more than five minutes per iteration. Total timeout for the file
-  // to appear is ~8.5 mins.
-  const unsigned MaxSeconds = 5*60;
+  // Don't wait more than 40s per iteration. Total timeout for the file
+  // to appear is ~1.5 minutes.
+  const unsigned MaxSeconds = 40;
   do {
     // Sleep for the designated interval, to allow the owning process time to
     // finish up and remove the lock file.