cmake-example: A hello world with CMake

A project just meant to demonstrate how CMake can be used as build
system.
Makefile: Rename MAKE_VERBOSE to V

To enable verbose messages form the build system use V=1 now.
Makefile: Reuse variables from echo for actual build

Currently the echoed commands and the commands actual used for building
where defined separately. Which could result in inconsistencies between
information printed to the screen and actually executed build steps.
Hence, reuse the same variables for printing and build.