users-guide: Make reverse flags addressable via :ghc-flag:
users-guide: Make reverse flags addressable via :ghc-flag:

Previously one could not easily link to the :reverse: flag of a
ghc-flag.

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc