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