Revert "cmake: Update to 2.8.11.2"

This breaks some packages (notably liblapack) due to a broken macro
(CTEST_CUSTOM_POST_TEST). See NixOS/nixpkgs#762

This reverts commit ebc424c3abfa72464c5f6777f2d522bf6d0f3790.

Signed-off-by: Shea Levy <shea@shealevy.com>