* tests/test-dprintf-posix.h: New file, extracted from
tests/test-dprintf-posix.c.
* tests/test-dprintf-posix.c: Include it. Don't include infinity.h.
(test_function): Remove function.
* modules/dprintf-posix-tests (Files): Add it.
* tests/test-dzprintf-posix.c: New file, based on
tests/test-dprintf-posix.c.
* tests/test-dzprintf-posix.sh: New file, based on
tests/test-dprintf-posix.sh.
* modules/dzprintf-posix-tests: New file.