[CMake] Removing default COMPILE_FLAGS

[Daniel Nelson]

I am building a project that has a single managed c++ target, and I need to
remove a compile flag for only this one target, since it conflicts with the -clr
flag.  Is it possible to remove a flag from the default CMAKE_CXX_FLAGS variable
only for this target?  Or do I have to remove the flag from the default flags
and add it in for every target except this one?