[llvm] [MLGO] Fix logging verbosity in scripts (PR #107818)

[Mircea Trofin via llvm-commits]

================
@@ -20,8 +20,8 @@
 
 To change the logging verbosity, pass an integer representing the desired
 verbosity to the --verbosity flag. Use 0 for all logs, status information,
-and detailed debug information, -1 for solely warnings, and -2 to not produce
-any output.
+and detailed debug information, 30 for solely warnings, and 50 or higher to
----------------
mtrofin wrote:

Let me put it differently: the documentation says there are really 3 settings: 
- very verbose
- warnings
- quiet

If not 0, -1, -2, how about an enum flag with those values?

https://github.com/llvm/llvm-project/pull/107818