* tests/test-printf-gnu.h (test_function): Use RETTYPE instead of 'int'.
* tests/test-printf-gnu.c (RETTYPE): New macro.
* tests/test-vprintf-gnu.c (RETTYPE): New macro.
* tests/test-vzprintf-gnu.c: New file, based on
tests/test-vprintf-gnu.c.
* tests/test-vzprintf-gnu.sh: New file, based on
tests/test-vprintf-gnu.sh.
* modules/vzprintf-gnu-tests: New file.
