Disable or customize CMAKE_{C,CXX}_FLAGS_{DEBUG,RELEASE} defaults
The default build types (Release, Debug,...) are adding compilation flags. User may want different compilation flags (for instance -O2 instead of -O3).
Using a custom type, without default flags, seems not to be an option as client code need to know the exact configuration name in order to link the right version of a library when using find_package. Forcing client to be aware of custom configurations is not a good way to promote a library usage...
Thus it should be to use Release and Debug config names without having the default flags.
Edited by Brad King