The testcase is just buggy; it assumes the target supports stabs, but should not do so. It should use some dg-require-stabs function alt. xfail all non-stabs targets (like this one; dwarf2 only) alt. compile on just a known set of stabs targets.
For the record, the .log message is: /gcc/testsuite/gcc.dg/20040813-1.c:1: error: target system does not support the "stabs" debug format -- Summary: mmix-knuth-mmixware testsuite failure: gcc.dg/20040813- 1.c Product: gcc Version: 4.0.0 Status: UNCONFIRMED Severity: normal Priority: P2 Component: target AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: hp at gcc dot gnu dot org CC: gcc-bugs at gcc dot gnu dot org GCC host triplet: i686-pc-linux-gnu GCC target triplet: mmix-knuth-mmixware http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18336