Add partial support for building/testing/benchmarking XNNPACK on Hexagon. Additional work would need to be done to get this fully working in the Bazel build (notably, connecting to a Qualcomm SDK) but this extends the basic build rules enough to add specializations for Hexagon to XNNPACK.

[copybara-service[bot]]

Add partial support for building/testing/benchmarking XNNPACK on Hexagon. Additional work would need to be done to get this fully working in the Bazel build (notably, connecting to a Qualcomm SDK) but this extends the basic build rules enough to add specializations for Hexagon to XNNPACK.