Who defines __GLASGOW_HASKELL__, __HADDOCK__, etc?

[Claus Reinke]

So far, I had assumed that every tool defined its own macro,
but it seems that __GLASGOW_HASKELL__ is defined by
ghc and by cabal, while __HADDOCK__ is defined only by
the latter. Is that right?

Context is http://trac.haskell.org/haddock/ticket/48 , ie, how
to adapt sources that had to bypass or help along haddock1
for haddock2 (which should need fewer workarounds).

Claus