mongodb 2.7.6 (devel)

Closes #32160.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
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.