[dvsim] Do not fail build step if build_fail_patterns matches, but exit code is 0

Nobody has claimed this yet.

FuseSoC returns a non-zero exit code it if failed, but a zero exit-code otherwise. If the exit code is 0, the STDOUT should be ignored and not parsed for additional error messages.

In https://github.com/lowRISC/opentitan/pull/6875 we disabled the fail patterns completely for the build step, but a better solution would be:

> I think a better approach is to look for the set fail patterns only if non-zero exit code is returned. That would of course apply only to the build step - simulation runs return zero exit code even the test actually failed so we do need to look for the error patterns in the log.

See https://github.com/lowRISC/opentitan/pull/6875 for detailed information on what caused this issue.

Start with the dvsim build-step handling and review the behavior described in pull request 6875. Verify that build output is handled differently for zero and non-zero exit codes, while simulation runs still use the configured error patterns; done means the build no longer fails on matching output when its exit code is zero.

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