cmake -DCMAKE_*_FLAGS*=<TAB>
will invoke _gcc as if one completes
export CPPFLAGS=<TAB>
Given that _gcc doesn't distinguish between CFLAGS, CPPFLAGS, or
CXXFLAGS, neither do we here.
https://cmake.org/cmake/help/v3.3/variable/CMAKE_PREFIX_PATH.html
* some packages provide no Find${PROJECT}.cmake file but a ${PROJECT}Config.cmake instead
* providing these through CMAKE_MODULE_PATH just results in an error
message, which points out one should've used CMAKE_PREFIX_PATH instead.
* added common properties for makefile verbosity
* options are picked from https://stackoverflow.com/a/2673355
* explanation strings from the cmake documentation