GCC: suppress unknown diagnostic pragma warning

'-Wdelete-non-abstract-non-virtual-dtor' is a clang-only
flag. Switch pragma diagnostic from GCC to clang.

Bug: None
Change-Id: Ic4488d9f95b351bcf74eeb4dba5bf568405948e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2279981Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#785322}

third_party/blink/renderer/platform/heap/finalizer_traits.h

@@ -43,10 +43,10 @@ struct FinalizerTraitImpl<T, true> {
 // an object's base class has a virtual destructor. In case there is no virtual
 // destructor present, the object is always finalized through its leaf type. In
 // other words: there is no finalization through a base pointer.
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wdelete-non-abstract-non-virtual-dtor"
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdelete-non-abstract-non-virtual-dtor"
       static_cast<T*>(obj)->~T();
-#pragma GCC diagnostic pop
+#pragma clang diagnostic pop
     }
   };
   using FinalizeImpl =