-Onot is not described in the GHC User's Guide, Version 6.6.1

[thorkilnaur]

The GHC optimization option -Onot is not described in the current (Version 6.6.1) GHC User's Guide, but it is nevertheless used, for example in mk/build.mk.sample in the GHC darcs repository. I would expect some description of -Onot in http://www.haskell.org/ghc/docs/latest/html/users_guide/options-optimise.html and a summary in http://www.haskell.org/ghc/docs/latest/html/users_guide/flag-reference.html. Interestingly, I have found this description in an earlier version of the User's Guide (http://www.haskell.org/ghc/docs/2.10/users_guide/user_26.html):

`-Onot':

This option will make GHC "forget" any -Oish options it has seen so far. Sometimes useful; for example: `make all EXTRA_HC_OPTS=-Onot'.

But what this really means, I am not sure.

[igloo]

It's a synonym for -O0, i.e. "do not optimise". As it's not documented at all, and sounds like it has been dedocumented at some point, I think we may as well consider it deprecated. I've added a comment to that effect, but we don't have the machinery for deprecated flag warnings currently.