[bugfix][cmake] install executables as targets
Installing the generated executables als FILES
resulted in the following
error message on Debian Stretch (CMake 3.7.2):
CMake Error at cmake_install.cmake:44 (file):
file INSTALL cannot find
"/home/nolte/numerics/master/dune-grid-howto/adaptivefinitevolume".
This patch fixes the issue by installing them as TARGETS
.