Cranelift AArch64: Fix the get_return_address lowering (#4851)

The previous implementation assumed that nothing had clobbered the
LR register since the current function had started executing, so
it would be incorrect for a non-leaf function, for example, that
contains the `get_return_address` operation right after a call.
The operation is valid only if the `preserve_frame_pointers` flag
is enabled, which implies that the presence of a frame record on
the stack is guaranteed.

Copyright (c) 2022, Arm Limited.

cranelift/codegen/src/machinst/isle.rs

@@ -743,6 +743,15 @@ macro_rules! isle_prelude_methods {
             }
         }
 
+        #[inline]
+        fn preserve_frame_pointers(&mut self) -> Option<()> {
+            if self.flags.preserve_frame_pointers() {
+                Some(())
+            } else {
+                None
+            }
+        }
+
         #[inline]
         fn func_ref_data(&mut self, func_ref: FuncRef) -> (SigRef, ExternalName, RelocDistance) {
             let funcdata = &self.lower_ctx.dfg().ext_funcs[func_ref];