cmake HAVE_GTK_UPDATE_ICON_CACHE_EXEC examples

quotient-im/Quaternion cmake/ECMInstallIcons.cmake :198 

install(CODE "
    set(DESTDIR_VALUE \"\$ENV{DESTDIR}\")
    if (NOT DESTDIR_VALUE)
        execute_process(COMMAND \"${CMAKE_COMMAND}\" -E touch \"${CMAKE_INSTALL_PREFIX}/${installdir}/${theme}\")
        set(HAVE_GTK_UPDATE_ICON_CACHE_EXEC ${GTK_UPDATE_ICON_CACHE_EXECUTABLE})
        if (HAVE_GTK_UPDATE_ICON_CACHE_EXEC)
            execute_process(COMMAND ${GTK_UPDATE_ICON_CACHE_EXECUTABLE} -q -t -i . WORKING_DIRECTORY \"${CMAKE_INSTALL_PREFIX}/${installdir}/${theme}\")
        endif ()
    endif (NOT DESTDIR_VALUE)
    ")