Reland "Avoid use of x18 register on arm64"

This is a reland of commit c2f25454.
We revert to using x17 for the call target, to be compliant with CFI.
Some comments are extended to point to that requirement.

Original change's description:
> Avoid use of x18 register on arm64
>
> This causes crashes on Windows, as x18 is the "platform register",
> holding a pointer to thread-local storage.
>
> R=jkummerow@chromium.org
> CC=seth.brenith@microsoft.com
>
> Bug: v8:12959
> Change-Id: I20b8bee145d4ab3a40d8d140d98572df8300251c
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3695569
> Reviewed-by: Seth Brenith <seth.brenith@microsoft.com>
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#81090}

Bug: v8:12959
Change-Id: If4ead8f7a7aece756cef7d32bb98d7d33dfe4911
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3702331Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Seth Brenith <seth.brenith@microsoft.com>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81111}

src/builtins/arm64/builtins-arm64.cc

@@ -3093,6 +3093,8 @@ void Builtins::Generate_WasmCompileLazy(MacroAssembler* masm) {
     return saved_fp_regs;
   })();
 
+  UseScratchRegisterScope temps(masm);
+  temps.Exclude(x17);
   {
     HardAbortScope hard_abort(masm);  // Avoid calls to Abort.
     FrameScope scope(masm, StackFrame::WASM_COMPILE_LAZY);
@@ -3109,7 +3111,7 @@ void Builtins::Generate_WasmCompileLazy(MacroAssembler* masm) {
     __ Mov(cp, Smi::zero());
     __ CallRuntime(Runtime::kWasmCompileLazy, 2);
 
-    // Untag the returned Smi into into x17, for later use.
+    // Untag the returned Smi into into x17 (ip1), for later use.
     static_assert(!kSavedGpRegs.has(x17));
     __ SmiUntag(x17, kReturnRegister0);
 
@@ -3119,12 +3121,14 @@ void Builtins::Generate_WasmCompileLazy(MacroAssembler* masm) {
   }
 
   // The runtime function returned the jump table slot offset as a Smi (now in
-  // x17). Use that to compute the jump target.
-  static_assert(!kSavedGpRegs.has(x18));
-  __ ldr(x18, MemOperand(
-                  kWasmInstanceRegister,
-                  WasmInstanceObject::kJumpTableStartOffset - kHeapObjectTag));
-  __ add(x17, x18, Operand(x17));
+  // x17). Use that to compute the jump target. Use x17 (ip1) for the branch
+  // target, to be compliant with CFI.
+  constexpr Register temp = x8;
+  static_assert(!kSavedGpRegs.has(temp));
+  __ ldr(temp, MemOperand(
+                   kWasmInstanceRegister,
+                   WasmInstanceObject::kJumpTableStartOffset - kHeapObjectTag));
+  __ add(x17, temp, Operand(x17));
   // Finally, jump to the jump table slot for the function.
   __ Jump(x17);
 }