Revert of Remove v8_toolset_for_d8 flag

src/d8.gyp

Index: src/d8.gyp
diff --git a/src/d8.gyp b/src/d8.gyp
index e60b01f8c847145c9c8c4d4875eb654151dace60..f328616238e8f2755a4b58f9a1466cea0a7174d3 100644
--- a/src/d8.gyp
+++ b/src/d8.gyp
@@ -31,6 +31,7 @@
     # Enable support for Intel VTune. Supported on ia32/x64 only
     'v8_enable_vtunejit%': 0,
     'v8_enable_i18n_support%': 1,
+    'v8_toolset_for_d8%': 'target',
   },
   'includes': ['../gypfiles/toolchain.gypi', '../gypfiles/features.gypi'],
   'targets': [
@@ -51,7 +52,7 @@
       ],
       'conditions': [
         [ 'want_separate_host_toolset==1', {
-          'toolsets': [ 'target', ],
+          'toolsets': [ '<(v8_toolset_for_d8)', ],
         }],
         ['(OS=="linux" or OS=="mac" or OS=="freebsd" or OS=="netbsd" \
            or OS=="openbsd" or OS=="solaris" or OS=="android" \
@@ -140,7 +141,7 @@
     },
   ],
   'conditions': [
-    ['test_isolation_mode != "noop"', {
+    ['test_isolation_mode != "noop" and v8_toolset_for_d8 == "target"', {
       'targets': [
         {
           'target_name': 'd8_run',