dg-skip-if usage problem

[Hans-Peter Nilsson]

I'm trying to skip the faulty gcc.dg/20040813-1.c for MMIX (see
PR target/18336).  It seems dg-skip-if should let me do that:
"Skip the test (report it as UNSUPPORTED) if the target list and
included flags are matched and the excluded flags are not
matched" but I don't know how how to use it, and existing usage
doesn't give me a working clue.  For example these permutations
don't work:
/* { dg-skip-if "" { mmix-*-* } { "" } { "" } } */
/* { dg-skip-if "" { mmix-*-* } { "" } { "-c" } } */
/* { dg-skip-if "" { mmix-*-* } { "-c" } { "" } } */
/* { dg-skip-if "" { mmix-*-* } { "-c" } { "-c" } } */
(plus some variants with "no-such-option").  Better would be
to add a dg-require-stabs, of course, but I still need a way to
skip a test, and I'm not happy with just xfailing it: "xfail" is
not "unsupported".

Help?

brgds, H-P