Implement basic C/CXX flag conglomeration
Implement basic C/CXX flag conglomeration

Provide basic collection and merging of warning, optimization and
debugging flags at end of CetCompilerSettings module. Call
cet_default_asserts on PROJECT_SOURCE_DIR and then enable assertions
on it if the user request that option.

drbenmorgan/cetbuildtools2,drbenmorgan/cetbuildtools2,drbenmorgan/cetbuildtools2