[llvm] [Offload] Implement event sync in amdgpu (PR #149300)

[Joseph Huber via llvm-commits]

================
@@ -1575,6 +1592,21 @@ struct AMDGPUEventTy {
     return Stream.waitEvent(*this);
   }
 
+  Error sync() {
+    std::lock_guard<std::mutex> Lock(Mutex);
----------------
jhuber6 wrote:

Can you explain the need for these mutexes? I'm just a little concerned when we have mutexes combined with functions that handle callbacks.

https://github.com/llvm/llvm-project/pull/149300