executor_runner on iOS fixes (#1364)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1364

A few fixes to the iOS benchmark
1. Ignore `-wShadow` since this was failing due to EXECUTORCH_SCOPE_PROF in the profiler/event tracer
2. Platform-specific headers in iOS build. Defining `IOS_BENCHMARK` in the `PyTorchBenchmark` build rule does not propagate to dependencies, so the `executor_runner_lib` was building without this definition
3. Remove deprecated `generate_etdump` flag from controlling program flow
4. Add build options to `PyTorchBenchmark` build config

Reviewed By: kirklandsign

Differential Revision: D51825112

fbshipit-source-id: d9734e255b3e6ea98412dbfb36a3be287ea38992