Add --architecture flag to theta

[leventeBajczi]

We have some wrong results regarding the architecture, because we didn't pass this flag to Theta beforehand. This fixes it.

[PhilippWendler]

Was --architecture already available in Theta previously, and just missing from the command line? Or is it new? In the latter case, the change would make old versions of Theta difficult to execute with BenchExec.

[leventeBajczi]

Was --architecture already available in Theta previously, and just missing from the command line? Or is it new? In the latter case, the change would make old versions of Theta difficult to execute with BenchExec.

This has been available to Theta since our original entry in SV-COMP 2022. We were debugging some erroneous results and it turned out we have been using ILP32 for every benchmark run, hence the wrong results. I think that all useful versions of Theta (which handle C verification somewhat well) handle this flag, so I'm not really worried about compatibility.