* rs6000-tdep.c (store_param_on_stack_p): New function,

        an improved version of some code extracted from skip_prologue().
        (skip_prologue): Use store_param_on_stack_p() to detect
        instructions saving a parameter on the stack. Detect when r0
        is used to save a parameter.
        Do not mark "li rx, SIMM" instructions as part of the prologue,
        unless the following instruction is also part of the prologue.