trace: [tcg] Generate TCG tracing routines

trace: [tcg] Generate TCG tracing routines

Generate header "trace/generated-tcg-tracers.h" with the necessary routines for
tracing events in guest code:

* trace_${event}_tcg

  Convenience wrapper that calls the translation-time tracer
  'trace_${event}_trans', and calls 'gen_helper_trace_${event}_exec to
  generate the TCG code to later trace the event at execution time.

Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>