LCC: Add policy CMP0129 regarding interpreting LCC as GNU
Due to MCST LCC compiler identification is now changed to LCC, there should be a way for old projects to still identify it as GNU, as it was before. This commits adds the policy: CMP0129: Compiler id for MCST LCC compilers is now LCC, not GNU. This policy controls such a behavior. OLD behaivior is to treat LCC as GNU, NEW is to treat is as LCC.