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/verifier/mod.rs

@@ -721,6 +721,26 @@ impl<'a> Verifier<'a> {
                     ));
                 }
             }
+            NullAry {
+                opcode: Opcode::GetFramePointer | Opcode::GetReturnAddress,
+            } => {
+                if let Some(isa) = &self.isa {
+                    if !isa.flags().preserve_frame_pointers() {
+                        return errors.fatal((
+                            inst,
+                            self.context(inst),
+                            "`get_frame_pointer`/`get_return_address` cannot be used without \
+                             enabling `preserve_frame_pointers`",
+                        ));
+                    }
+                } else {
+                    return errors.fatal((
+                        inst,
+                        self.context(inst),
+                        "`get_frame_pointer`/`get_return_address` require an ISA!",
+                    ));
+                }
+            }
             Unary {
                 opcode: Opcode::Bitcast,
                 arg,