Features committed in 2016 have required cmake verison 2.8.11.
`sergiu Tue Nov 22 12:25:06 2016 +0100: target_compile_definitions`
Set the minimum cmake version to the minimum version that
is capable of compiling or installing the code base.
Ancient versions of CMake required else(), endif(), and similar block
termination commands to have arguments matching the command starting the block.
This is no longer the preferred style.
