[llvm] [Offload] Implement `olShutDown` (PR #144055)

[Ross Brunton via llvm-commits]

================
@@ -191,18 +193,41 @@ Error initPlugins() {
   return Plugin::success();
 }
 
-// TODO: We can properly reference count here and manage the resources in a more
-// clever way
 Error olInit_impl() {
-  static std::once_flag InitFlag;
-  std::optional<Error> InitResult{};
-  std::call_once(InitFlag, [&] { InitResult = initPlugins(); });
+  std::lock_guard<std::mutex> Lock{OffloadContextValMutex};
+
+  std::optional<Error> InitResult;
+  if (!isOffloadInitialized())
+    InitResult = initPlugins();
+
+  OffloadContext::get().RefCount++;
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RossBrunton wrote:

The context is `new`'d in `initPlugins()`, but perhaps it makes sense doing it in `olInit_impl`, so I'll move it here.

https://github.com/llvm/llvm-project/pull/144055