[D1] more configurable -v2 output

* -v2 does not imply -wi anymore, explicit -w / -wi usage is expected
* -v2=xxx allows to enabled only specific warnings
* -v2-list prints all available -v2 warning kinds

All this stuff is needed for fine tuning of -v2 output and compiler
exit status codes in project Jenkins jobs (to ensure regression control
for -v2 changes)
Above 2 lines: conversion => conversion