Refine the behaviour of -dno-debug-output and -dtrace-level
It wasn't clear to me what these flags should do and what they should turn off.
From the user guide.
|`-dno-debug-output`||Suppress any unsolicited debugging output. When GHC has been built with the DEBUG option it occasionally emits debug output of interest to developers. The extra output can confuse the testing framework and cause bogus test failures, so this flag is provided to turn it off.|
-dno-debug-output currently suppresses the output of
-ddump-tc-trace which is certainly not "unsolicited". It should be used, and is, in
Outputable to suppress the output of
dtrace-level is used in a few places but always as if was a boolean flag. I don't really see what the point of it is. The only commit which mentions it is "8cdb98b9" and I can't find the origin of the flag. I think we should just remove it.