[CMake] Cleaning up CMake version checks in ExternalProject calls

Now that we're on CMake 3.4.3 all the ExternalProject features we use are supported everywhere, so we don't need the version checks anymore.

llvm-svn: 272324
GitOrigin-RevId: f325b8c71b04d8fd42c59bc0023c1aed17c53f4c
2 files changed