Prepare for integration into ICON

.gitmodules

CMakeLists.txt

cmake/eccodes-config.cmake

cmake/eckit-config.cmake

cmake/fdb-config.cmake

cmake/healpix_cxx-config.cmake

cmake/libcdi-config.cmake

cmake/libfyaml-config.cmake

cmake/mtime-config.cmake

cmake/yac-config.cmake

cmake/yaxt-config.cmake

external/libcdi

external/yac

external/yaxt