diagnostics: Fix PR 15378

[Joseph S. Myers]

On Mon, 30 Aug 2004, Gabriel Dos Reis wrote:

> I did not attach a testcase because our testsuite infrastructure looks
> for line numbers, and we don't have one for this kind of thing.

Try using line number 0:

/* { dg-error "warnings being treated as errors" "" { target *-*-* } 0 } */

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Joseph S. Myers               http://www.srcf.ucam.org/~jsm28/gcc/
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