Cleanup GHC verbosity flags
- In the discussion of D2679#77898, Simon Marlow suggested that we make verbosity levels (
-v1...) work just like optimization levels (
-O1...), i.e., that we make each verbosity level a collection of verbosity flags.
Currently the verbosity level is tested against explicitly in several places in GHC's code.
- Homogenize verbosity flags: currently, flags that change GHC's reporting have various prefixes:
Maybe we should homogenize (some of) them by using a common
-v prefix as in