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/filetests/filetests/isa/aarch64/fp_sp_pc-pauth.clif

@@ -0,0 +1,47 @@
+test compile precise-output
+set preserve_frame_pointers=true
+target aarch64 sign_return_address
+
+function %fp() -> i64 {
+block0:
+    v0 = get_frame_pointer.i64
+    return v0
+}
+
+;   paciasp
+;   stp fp, lr, [sp, #-16]!
+;   mov fp, sp
+; block0:
+;   mov x0, fp
+;   ldp fp, lr, [sp], #16
+;   autiasp ; ret
+
+function %sp() -> i64 {
+block0:
+    v0 = get_stack_pointer.i64
+    return v0
+}
+
+;   paciasp
+;   stp fp, lr, [sp, #-16]!
+;   mov fp, sp
+; block0:
+;   mov x0, sp
+;   ldp fp, lr, [sp], #16
+;   autiasp ; ret
+
+function %return_address() -> i64 {
+block0:
+    v0 = get_return_address.i64
+    return v0
+}
+
+;   paciasp
+;   stp fp, lr, [sp, #-16]!
+;   mov fp, sp
+; block0:
+;   ldr lr, [fp, #8]
+;   xpaclri
+;   mov x0, lr
+;   ldp fp, lr, [sp], #16
+;   autiasp ; ret

cranelift/filetests/filetests/isa/aarch64/fp_sp_pc.clif

@@ -37,7 +37,6 @@ block0:
 ;   stp fp, lr, [sp, #-16]!
 ;   mov fp, sp
 ; block0:
-;   mov x0, lr
+;   ldr x0, [fp, #8]
 ;   ldp fp, lr, [sp], #16
 ;   ret
-