[heap] Adjust condition for enabling concurrent marking.

This changes CPU check to use 'target_cpu' instead of 'v8_target_cpu'.

Bug: chromium:694255
Change-Id: Ic3ad5253e4e0b66b13e9f16a5842bcf49881fa52
Reviewed-on: https://chromium-review.googlesource.com/677994Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48119}

BUILD.gn

@@ -151,7 +151,7 @@ if (v8_check_microtasks_scopes_consistency == "") {
   v8_check_microtasks_scopes_consistency = is_debug || dcheck_always_on
 }
 if (v8_enable_concurrent_marking == "") {
-  if (v8_target_cpu == "x86" || v8_target_cpu == "x64") {
+  if (target_cpu == "x86" || target_cpu == "x64") {
     v8_enable_concurrent_marking = true
   } else {
     v8_enable_concurrent_marking = false

gypfiles/features.gypi

@@ -83,7 +83,7 @@
 
     # Enable concurrent marking.
     'conditions': [
-      ['v8_target_arch=="x64" or v8_target_arch=="ia32"', {
+      ['target_arch=="x64" or target_arch=="ia32"', {
         'v8_enable_concurrent_marking%': 1,
       },{
         'v8_enable_concurrent_marking%': 0,