Produce smaller JSON blob

[lambdageek]

See lambdageek/centrinel-report#1

It may make sense to produce a single JSON file per translation unit and update centrinel-report to consume some version of the compile_commands.json database.

(would also have to munge the commands db before processing to note multiple invokes on a single translation unit)

[lambdageek]

This is done now. We traverse compile_commands.json and group all compile invocations on the same translation unit to avoid repeated work.