Land chromium-side work to clean up handling of v8_target_cpu in the GN build.

build/toolchain/gcc_toolchain.gni

 # Copyright (c) 2013 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/clang/clang.gni")
 import("//build/config/nacl/config.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/toolchain/cc_wrapper.gni")
 import("//build/toolchain/goma.gni")
 import("//build/toolchain/toolchain.gni")
@@ skipping 81 matching lines @@
 #      cc_wrapper = "" in it.
 #  - use_debug_fission
 #      Override the global use_debug_fission setting, useful if the particular
 #      toolchain should not be generating split-dwarf code.
 #  - use_goma
 #      Override the global use_goma setting, useful to opt-out of goma in a
 #      particular toolchain by setting use_gome = false in it.
 #  - use_gold
 #      Override the global use_gold setting, useful if the particular
 #      toolchain has a custom link step that is not actually using Gold.
+#  - v8_toolchain_cpu
+#      If defined, set v8_current_cpu to this, else set v8_current_cpu
+#      to current_cpu.
 template("gcc_toolchain") {
   toolchain(target_name) {
     assert(defined(invoker.ar), "gcc_toolchain() must specify a \"ar\" value")
     assert(defined(invoker.cc), "gcc_toolchain() must specify a \"cc\" value")
     assert(defined(invoker.cxx), "gcc_toolchain() must specify a \"cxx\" value")
     assert(defined(invoker.ld), "gcc_toolchain() must specify a \"ld\" value")
     assert(defined(invoker.toolchain_cpu),
            "gcc_toolchain() must specify a \"toolchain_cpu\"")
     assert(defined(invoker.toolchain_os),
            "gcc_toolchain() must specify a \"toolchain_os\"")
@@ skipping 346 matching lines @@
       }
       if (defined(invoker.use_debug_fission)) {
         use_debug_fission = invoker.use_debug_fission
       }
       if (defined(invoker.use_gold)) {
         use_gold = invoker.use_gold
       }
       if (defined(invoker.use_sysroot)) {
         use_sysroot = invoker.use_sysroot
       }
+      if (defined(invoker.v8_toolchain_cpu)) {
+        v8_current_cpu = invoker.v8_toolchain_cpu
+      } else {
+        v8_current_cpu = current_cpu
+      }
 
       # Disable sanitizers for non-default toolchains.
       is_asan = false
       is_cfi = false
       is_lsan = false
       is_msan = false
       is_syzyasan = false
       is_tsan = false
       is_ubsan = false
       is_ubsan_null = false
@@ skipping 38 matching lines @@
     cxx = "$prefix/clang++"
     ld = cxx
     is_clang = true
 
     readelf = "${toolprefix}readelf"
     ar = "${toolprefix}ar"
     nm = "${toolprefix}nm"
 
     forward_variables_from(invoker,
                            [
+                             "strip",
                              "toolchain_cpu",
                              "toolchain_os",
                              "use_gold",
-                             "strip",
+                             "v8_toolchain_cpu",
                            ])
 
     if (defined(invoker.use_debug_fission)) {
       use_debug_fission = invoker.use_debug_fission
     }
   }
 }