liblzma: Fix mythread_sync for nested locking.
diff --git a/src/common/mythread.h b/src/common/mythread.h
index c538dea..637b8ac 100644
--- a/src/common/mythread.h
+++ b/src/common/mythread.h
@@ -70,8 +70,9 @@
/// things down at all compared to plain pthread_mutex_lock(&mutex)
/// and pthread_mutex_unlock(&mutex) calls.
///
-#define mythread_sync(mutex) mythread_sync_helper(mutex, __LINE__)
-#define mythread_sync_helper(mutex, line) \
+#define mythread_sync(mutex) mythread_sync_helper1(mutex, __LINE__)
+#define mythread_sync_helper1(mutex, line) mythread_sync_helper2(mutex, line)
+#define mythread_sync_helper2(mutex, line) \
for (unsigned int mythread_i_ ## line = 0; \
mythread_i_ ## line \
? (pthread_mutex_unlock(&(mutex)), 0) \
