tracepoints: Add support for CONDITION events

tracepoints: Add support for CONDITION events

These are events that check a condition before raising callbacks, but
take no hit for the condition when not tracing.  We don't have to do
anything special in stap except handle the new macro, as the condition
is handled at the trace site.

* tapsets.cxx (tracepoint_builder::get_tracequery_modules): Add a
  definition for DECLARE_TRACE_CONDITION.  Also settle the macro-
  arg wrappers to PARAMS().