i#2065 icache sync: Call machine_cache_sync in shared_gencode_emit.
i#2065 icache sync: Call machine_cache_sync in shared_gencode_emit.

This seems to cure the occasional failure of client.null_instrument
with a SIGILL that was observed on some systems with 64K pages.

Review-URL: https://codereview.appspot.com/315870043

AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio,AmesianX/dynamorio