Shared code shouldn't reference the platform specific method frame::interpreter_frame_last_sp()

The method `frame::interpreter_frame_last_sp()` is a platform method in the sense that it is not declared in a shared header file. It is declared and defined on some platforms though (x86 and aarch64 I think).

`frame::interpreter_frame_last_sp()` existed on these platforms before vm continuations (aka loom). Shared code that is part of the vm continuations implementation references it. This breaks the platform abstraction.