[llvm] [ORC] Fix synchronization in CoreAPIsTest. (PR #144556)

[Jameson Nash via llvm-commits]

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@@ -1559,16 +1559,13 @@ TEST_F(CoreAPIsStandardTest, TestLookupWithThreadedMaterialization) {
 #if LLVM_ENABLE_THREADS
 
   std::mutex WorkThreadsMutex;
-  std::vector<std::thread> WorkThreads;
+  SmallVector<std::thread,0> WorkThreads;
   DispatchOverride = [&](std::unique_ptr<Task> T) {
-    std::promise<void> WaitP;
-    std::lock_guard<std::mutex> Lock(WorkThreadsMutex);
+    std::unique_lock Lock(WorkThreadsMutex);
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vtjnash wrote:

FWIW, it looks like LLVM now may consider `lock_guard` deprecated in favor of drive-by replacements of it with `unique_lock` everywhere? #126434 #146240

https://github.com/llvm/llvm-project/pull/144556