Adds blocking file locks.

runtime/bin/file_macos.cc

Index: runtime/bin/file_macos.cc
diff --git a/runtime/bin/file_macos.cc b/runtime/bin/file_macos.cc
index 941d419352b64e904631ada3b4041d1942d37e05..a43b14eaada0245797ae855c2abde869b97e682c 100644
--- a/runtime/bin/file_macos.cc
+++ b/runtime/bin/file_macos.cc
@@ -139,9 +139,11 @@ bool File::Lock(File::LockType lock, int64_t start, int64_t end) {
       fl.l_type = F_UNLCK;
       break;
     case File::kLockShared:
+    case File::kLockBlockingShared:
       fl.l_type = F_RDLCK;
       break;
     case File::kLockExclusive:
+    case File::kLockBlockingExclusive:
       fl.l_type = F_WRLCK;
       break;
     default:
@@ -150,9 +152,12 @@ bool File::Lock(File::LockType lock, int64_t start, int64_t end) {
   fl.l_whence = SEEK_SET;
   fl.l_start = start;
   fl.l_len = end == -1 ? 0 : end - start;
-  // fcntl does not block, but fails if the lock cannot be acquired.
-  int rc = fcntl(handle_->fd(), F_SETLK, &fl);
-  return rc != -1;
+  int cmd = F_SETLK;
+  if ((lock == File::kLockBlockingShared) ||
+      (lock == File::kLockBlockingExclusive)) {
+    cmd = F_SETLKW;
+  }
+  return TEMP_FAILURE_RETRY(fcntl(handle_->fd(), cmd, &fl)) != -1;
 }