tests: avoid empty AT_DATA contents, for zsh.

tests: avoid empty AT_DATA contents, for zsh.

* tests/libtoolize.at (libtoolize macro serial update)
(libtoolize config files serial update, LIBTOOLIZE_OPTIONS):
Do not create empty files with AT_DATA, the latter is documented
to require a final newline.  Fixes testsuite failures with zsh
4.3.10.

Signed-off-by: Ralf Wildenhues <Ralf.Wildenhues@gmx.de>