tests: check the return value of personality when errno is not set (#6752)

The `personality` wrapper might not set errno, so in that case the return value
should be checked instead.

For details, see
https://sourceware.org/git/?p=glibc.git;a=commitdiff;h=e0043e17dfc52fe1702746543127cb4a87232bcd.

Closes #6737.