LLDB was not handling properly PPC64 functions that were entered using the local entry point, instead of the global one.
This was fixed by introducing a new function in the Architecture class, with an implementation for PPC64 that is able to properly handle the "skip past prologue" part of step-in.
There was also another related issue found: setting function breakpoints in PPC64. For functions with more than one entry point, the breakpoint was always being placed in function's global entry point, that would not be hit when the function was entered through a local context.
This was also fixed with a new Architecture function, that lets the plugin implementation to adjust the breakpoint address, which PPC64 uses to move the it to the local entry point, that is guaranteed to be hit even when entering the function through the global entry point.