[mlir] Do not start threads in AsyncRuntime

pthreads is not enabled for all builds by default

Reviewed By: jpienaar

Differential Revision: https://reviews.llvm.org/D89967

mlir/lib/ExecutionEngine/AsyncRuntime.cpp

@@ -59,8 +59,7 @@ mlirAsyncRuntimeAwaitToken(AsyncToken *token) {
 
 extern "C" MLIR_ASYNCRUNTIME_EXPORT void
 mlirAsyncRuntimeExecute(CoroHandle handle, CoroResume resume) {
-  std::thread thread([handle, resume]() { (*resume)(handle); });
-  thread.detach();
+  (*resume)(handle);
 }
 
 extern "C" MLIR_ASYNCRUNTIME_EXPORT void