cabal-install: Anticipate and fix GHC 7.8 bug.
cabal-install: use the same compiler (preprocessor) as ghc
cabal-install: update 1.20.0.3_1 bottle.

Closes #32165.
ruby-build 20140908
cabal-install: update 1.20.0.3_1 bottle.
ruby-build: add 20140908 bottle.