Revert "Raising minimum required CMake version to 2.8.12.2."

This reverts commit r230062.

Debian stable (wheezy) ships still with cmake 2.8.9.

The commit broke my LLVM/Polly buildbot, to my knowledge our only Linux+cmake
buildbot.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@230343 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed