[LockFileManager] Make default waitForUnlock timeout a parameter, NFC

Patch by Xi Ge!
diff --git a/llvm/lib/Support/LockFileManager.cpp b/llvm/lib/Support/LockFileManager.cpp
index 1018119..5c6508c 100644
--- a/llvm/lib/Support/LockFileManager.cpp
+++ b/llvm/lib/Support/LockFileManager.cpp
@@ -290,7 +290,8 @@
   sys::DontRemoveFileOnSignal(UniqueLockFileName);
 }
 
-LockFileManager::WaitForUnlockResult LockFileManager::waitForUnlock() {
+LockFileManager::WaitForUnlockResult
+LockFileManager::waitForUnlock(const unsigned MaxSeconds) {
   if (getState() != LFS_Shared)
     return Res_Success;
 
@@ -301,9 +302,6 @@
   Interval.tv_sec = 0;
   Interval.tv_nsec = 1000000;
 #endif
-  // 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.