GHS: Document usage of GHS_NO_SOURCE_GROUP_FILE
Document usage of GHS_NO_SOURCE_GROUP_FILE and CMAKE_GHS_NO_SOURCE_GROUP_FILE. This also changed the variable name to CMAKE_GHS_NO_SOURCE_GROUP_FILE.
Document usage of GHS_NO_SOURCE_GROUP_FILE and CMAKE_GHS_NO_SOURCE_GROUP_FILE. This also changed the variable name to CMAKE_GHS_NO_SOURCE_GROUP_FILE.