compiler/options.m:
Add --inst-statistics as a developer-only option.
compiler/hlds_statistics.m:
Add code to gather and write out statistics about how frequently
each function symbol of the mer_inst type occurs in (a) the instmaps
of procedures' goals, and (b) in the automatically generated inst
tables.
compiler/mercury_compile_front_end.m:
Invoke the new code if the new option is specified.
(The code to do so is a near-copy of the nearby code for invoking
the other functionality in hlds_statistics.m.)
tools/inst_stats:
Add this tool for summarizing the statistics generated by the new option.
