message: Attempt to fix build errors in MLIR transofmration.
  This transformation pass seems to break on g++ 5.4. The commit attempts to
  fix it. At least //tensorflow/compiler/... now pass after this commit.
diff: @@ -43,7 +43,7 @@ namespace {
  // IslandType is an enum representing if an island is the island (parent)
  // merging another island or is the island (child) being being merged.
  -enum class IslandType : bool { kParentIsland, kChildIsland };
  +enum IslandType { kParentIsland, kChildIsland };
  // Output is a helper struct holding a result index and island type (parent or
  // child).
  