* tests/test-fprintf-posix.h (test_function): Use RETTYPE instead of
'int'.
* tests/test-fprintf-posix.c (RETTYPE): New macro.
* tests/test-vdprintf-posix.c (RETTYPE): New macro.
* tests/test-vfprintf-posix.c (RETTYPE): New macro.
* tests/test-xfprintf-posix.c (RETTYPE): New macro.
* tests/test-vdzprintf-posix.c: New file, based on
tests/test-vdprintf-posix.c.
* tests/test-vdzprintf-posix.sh: New file, based on
tests/test-vdprintf-posix.sh.
* modules/vdzprintf-posix-tests: New file.