[GYP] Move builtins generation into mksnapshot

Bug:v8:6055

Change-Id: Ifeac048e5bee2d1782cdaaabe9f5257129b7be0e
Reviewed-on: https://chromium-review.googlesource.com/508528Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Loo Rong Jie <loorongjie@gmail.com>
Cr-Commit-Position: refs/heads/master@{#45437}

test/cctest/cctest.gyp

@@ -444,6 +444,9 @@
         }, {
           'dependencies': ['../../src/v8.gyp:v8'],
         }],
+        ['v8_use_snapshot=="true"', {
+          'dependencies': ['../../src/v8.gyp:v8_builtins_generators'],
+        }],
       ],
     },
     {

test/unittests/unittests.gyp

@@ -264,6 +264,9 @@
             '<(icu_gyp_path):icuuc',
           ],
         }],
+        ['v8_use_snapshot=="true"', {
+          'dependencies': ['../../src/v8.gyp:v8_builtins_generators'],
+        }],
       ],
     },
   ],