[arm64] Fix unused function error

Landing this simple fix rather than reverting

Tbr: rmcilroy@chromium.org

No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I230300c32bf6a97cd82376c46461735dd34378b9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2237632
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68262}

src/codegen/arm64/assembler-arm64.cc

@@ -41,6 +41,9 @@
 namespace v8 {
 namespace internal {
 
+namespace {
+
+#ifdef USE_SIMULATOR
 static unsigned SimulatorFeaturesFromCommandLine() {
   if (strcmp(FLAG_sim_arm64_optional_features, "none") == 0) {
     return 0;
@@ -57,6 +60,7 @@ static unsigned SimulatorFeaturesFromCommandLine() {
           "                       all\n");
   FATAL("sim-arm64-optional-features");
 }
+#endif  // USE_SIMULATOR
 
 static constexpr unsigned CpuFeaturesFromCompiler() {
   unsigned features = 0;
@@ -66,6 +70,8 @@ static constexpr unsigned CpuFeaturesFromCompiler() {
   return features;
 }
 
+}  // namespace
+
 // -----------------------------------------------------------------------------
 // CpuFeatures implementation.