gn: Switch off neon for V8 arm simulator builds

build/config/arm.gni

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/v8_target_cpu.gni")
 
 # These are primarily relevant in current_cpu == "arm" contexts, where
 # ARM code is being compiled.  But they can also be relevant in the
 # other contexts when the code will change its behavior based on the
 # cpu it wants to generate code for.
 if (current_cpu == "arm" || v8_current_cpu == "arm") {
   declare_args() {
     # Version of the ARM processor when compiling on ARM. Ignored on non-ARM
     # platforms.
     arm_version = 7
 
     # The ARM floating point mode. This is either the string "hard", "soft", or
     # "softfp". An empty string means to use the default one for the
     # arm_version.
     arm_float_abi = ""
 
     # The ARM variant-specific tuning mode. This will be a string like "armv6"
     # or "cortex-a15". An empty string means to use the default for the
     # arm_version.
     arm_tune = ""
 
     # Whether to use the neon FPU instruction set or not.
-    arm_use_neon = true
+    arm_use_neon = ""
 
     # Whether to enable optional NEON code paths.
     arm_optionally_use_neon = false
 
     # Thumb is a reduced instruction set available on some ARM processors that
     # has increased code density.
     arm_use_thumb = true
   }
 
   assert(arm_float_abi == "" || arm_float_abi == "hard" ||
          arm_float_abi == "soft" || arm_float_abi == "softfp")
 
+  if (arm_use_neon == "") {
+    if (current_os == "linux" && current_cpu != v8_current_cpu) {
+      # Don't use neon on V8 simulator builds as a default.
+      arm_use_neon = false
+    } else {
+      arm_use_neon = true
+    }
+  }
+
   if (arm_version == 6) {
     arm_arch = "armv6"
     if (arm_tune != "") {
       arm_tune = ""
     }
     if (arm_float_abi == "") {
       arm_float_abi = "softfp"
     }
     arm_fpu = "vfp"
     arm_use_thumb = false
@@ skipping 37 matching lines @@
       arm_fpu = "neon"
     } else {
       arm_fpu = "vfpv3-d16"
     }
   }
 } else if (current_cpu == "arm64" || v8_current_cpu == "arm64") {
   # arm64 supports only "hard".
   arm_float_abi = "hard"
   arm_use_neon = true
 }