[llvm] [Parallel] Revert sequential task changes (PR #109084)

[Fangrui Song via llvm-commits]

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@@ -99,7 +99,12 @@ TEST(Parallel, TaskGroupSequentialFor) {
   {
     parallel::TaskGroup tg;
     for (size_t Idx = 0; Idx < 500; Idx++)
-      tg.spawn([&Count, Idx]() { EXPECT_EQ(Count++, Idx); }, true);
+      tg.spawn(
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MaskRay wrote:

Thx. I just realized that build failure of the unittest. Deleted:)

https://github.com/llvm/llvm-project/pull/109084