c++/10569: use typedef type as return from main yields warning

[Wolfgang Bangerth]

> There's something weird going on, though. For me, it fails with
> *error* when turning on -Wall, but not when additionally giving
> -pedantic:

Yes, that's a well know problem: -pedantic downgrades some errors to 
warnings.

W.

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Wolfgang Bangerth              email:            bangerth@ices.utexas.edu
                               www: http://www.ices.utexas.edu/~bangerth/