Cranelift: Add instructions for getting the current stack/frame/return pointers (#4573)

* Cranelift: Add instructions for getting the current stack/frame pointers and return address

This is the initial part of https://github.com/bytecodealliance/wasmtime/issues/4535

* x64: Remove `Amode::RbpOffset` and use `Amode::ImmReg` instead

We just special case getting operands from `Amode`s now.

* Fix s390x `get_return_address`; require `preserve_frame_pointers=true`

* Assert that `Amode::ImmRegRegShift` doesn't use rbp/rsp

* Handle non-allocatable registers in Amode::with_allocs

* Use "stack" instead of "r15" on s390x

* r14 is an allocatable register on s390x, so it shouldn't be used with `MovPReg`

cranelift/codegen/src/isa/aarch64/lower.isle

@@ -1697,6 +1697,7 @@
 
 
 ;;;; Rules for `uunarrow` ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
 (rule (lower (has_type (ty_vec128_int ty) (uunarrow x y)))
       (if (zero_value y))
       (uqxtn x (lane_size ty)))
@@ -1733,3 +1734,14 @@
 
 (rule (lower (debugtrap))
       (side_effect (brk)))
+
+;;; Rules for `get_{frame,stack}_pointer` and `get_return_address` ;;;;;;;;;;;;;
+
+(rule (lower (get_frame_pointer))
+      (aarch64_fp))
+
+(rule (lower (get_stack_pointer))
+      (aarch64_sp))
+
+(rule (lower (get_return_address))
+      (aarch64_link))