#561 Use pop longmen for stm8

[Philipp Klaus Krause]

The stm8 backend should make use of the pop longmen instruction. Something like the peephole

}
    pop a
    ld  %1, a
} by {
    pop %1
}

Either as a peephole (but how would it know that %1 is a global variable?) or in code generation (but the pop usually comes from a call, then the ld from an assignment, so two different iCodes).

Philipp