Clean up install rules of CMake itself (#14371)
Ensure CMAKE_DATA_DIR, CMAKE_DOC_DIR, and CMAKE_MAN_DIR are always relative paths in CMake code, and set defaults accordingly. Use the install() command instead of install_files() and install_targets(). This is more modern and also avoids stripping of the first character from user-specified destinations. While at it, fix the default destinations reported in the bootstrap help.
Showing with 41 additions and 42 deletions