[CMake] Set different compilation flags for specific file

[James Bigler]

I have a file that doesn't compile properly with certain optimization flags that 
I wish to use on the rest of my system.  I poked around the wiki and the help 
file, but I can't find any information on how to do this.

According to the documentation SET_SOURCE_FILES_PROPERTIES COMPILE_FLAGS only 
appends new flags.  I want to override the values in CMAKE_CXX_FLAGS and 
CMAKE_CXX_FLAGS_RELEASE.

Thanks,
James