#3993 uc6502 --stack-auto issue

[Philipp Klaus Krause]

The attached "regression test" originated from an attempt to reproduce a z88dk bug in sdcc (I guess the underlying issue in the z80 backend has been fixed since SDCC 4.5.0, and I was never able to reproduce the issue), but it turns out to fail for the test-uc6502-stack-auto regression test target.