Fix linux

test/cpp/microbenchmarks/bm_pollset.cc

@@ -45,6 +45,8 @@ extern "C" {
 #include "test/cpp/microbenchmarks/helpers.h"
 #include "third_party/benchmark/include/benchmark/benchmark.h"
 
+#include <string.h>
+
 auto& force_library_initialization = Library::get();
 
 static void shutdown_ps(grpc_exec_ctx* exec_ctx, void* ps, grpc_error* error) {