CMake: Allow using symlinks for installed files. (#19043)

* CMake: Allow using symlinks for installed files.

cMake/FreeCAD_Helpers/InitializeFreeCADBuildOptions.cmake

@@ -15,6 +15,7 @@ macro(InitializeFreeCADBuildOptions)
     option(BUILD_WITH_CONDA "Set ON if you build FreeCAD with conda" OFF)
     option(BUILD_DYNAMIC_LINK_PYTHON "If OFF extension-modules do not link against python-libraries" ON)
     option(INSTALL_TO_SITEPACKAGES "If ON the freecad root namespace (python) is installed into python's site-packages" ON)
+    option(INSTALL_PREFER_SYMLINKS "If ON then fc_copy_sources macro will create symlinks instead of copying files" OFF)
     option(OCCT_CMAKE_FALLBACK "disable usage of occt-config files" OFF)
     if (WIN32 OR APPLE)
         option(FREECAD_USE_QT_FILEDIALOG "Use Qt's file dialog instead of the native one." OFF)

cMake/FreeCadMacros.cmake

@@ -9,12 +9,18 @@ MACRO (fc_copy_sources target_name outpath)
 	else()
 		set(fc_details "")
 	endif()
+	if(INSTALL_PREFER_SYMLINKS)
+		set(copy_command create_symlink)
+	else()
+		set(copy_command copy)
+	endif()
+
 	foreach(it ${ARGN})
 		get_filename_component(infile ${it} ABSOLUTE)
 		get_filename_component(outfile "${outpath}/${it}" ABSOLUTE)
 		add_file_dependencies("${infile}" "${outfile}")
 		ADD_CUSTOM_COMMAND(
-			COMMAND   "${CMAKE_COMMAND}" -E copy "${infile}" "${outfile}"
+			COMMAND   "${CMAKE_COMMAND}" -E ${copy_command} "${infile}" "${outfile}"
 			OUTPUT   "${outfile}"
 			COMMENT "Copying ${infile} to ${outfile}${fc_details}"
 			MAIN_DEPENDENCY "${infile}"