Suppress clang warning "ATOMIC_FLAG_INIT marked deprecated" (#1502)

In C++20, macro 'ATOMIC_FLAG_INIT' has been marked as deprecated.
We need still to use it to be able to compile for C++17.
For now, just suppress this warning.

tdutils/td/utils/SpinLock.h

@@ -63,7 +63,10 @@ class SpinLock {
   }
 
  private:
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-pragma"
   std::atomic_flag flag_ = ATOMIC_FLAG_INIT;
+#pragma clang diagnostic pop
   void unlock() {
     flag_.clear(std::memory_order_release);
   }