[clang] [clang-tools-extra] [clang] Reference-count `ModuleCache` non-intrusively (PR #164889)

[Jan Svoboda via cfe-commits]

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@@ -12,6 +12,7 @@
 #include "clang/Serialization/ModuleCache.h"
 #include "llvm/ADT/StringMap.h"
 
+#include <atomic>
----------------
jansvoboda11 wrote:

This file uses `std::atomic`, but it was relying on a transitive include of `<atomic>` from "IntrusiveRefCntPtr.h" via "ModuleCache.h". Since `ModuleCache` now isn't ref-counted intrusively, it dropped the include, causing this.

https://github.com/llvm/llvm-project/pull/164889