by -DHAVE_CONFIG_H.
* MODULES.html.sh (Support for building libraries and executables):
Add config-h.
* modules/config-h: New file.
* gnulib-tool (nl, sed_transform_lib_file): New vars.
(func_import): Turn "#ifdef HAVE_CONFIG_H" to "#if 1" if
the config-h module is used.
* m4/config-h.m4: New file.