Automatically added Tracepoints are added to ModGuts.

This is a [Tracepoint] list for all the Tracepoints in a given
module. Nothing uses this list of Tracepoints yet, but it will be
required for Backtrace support in the  Code Generator.
Added empty module StgCmmBacktrace.

This module will contain functions for backtrace support in the Code Generator.
Code Generator creates static Tracepoints in the produced binary.

* Thread modTracepoints through from modGuts to cgGuts
* Thread modTracepoints through from cgGuts to initTracepoints
* initTracepoints generates CmmLits containing all the information in
  each tracepoint.