CodeBlocks: add option for the CB compiler ID

CodeBlocks uses his own compiler ID string which may differ from CMAKE_<LANG>_COMPILER_ID. In particular CodeBlocks supports a large number of different compiler configurations (with different IDs) This commit adds a cache variable "CMAKE_CODEBLOCKS_COMPILER_ID", so the user might adjust it when needed.

Unfortunately there is a slight difference in the behavior: The new version only considers languages mentioned in the project command. The old version considered all enabled languages, those mentioned in the enable_language as well as in the project command. Of course the new behavior also does not reflect changes made in the enabled languages after the first configuration as the variable is cached.