Fix BUILD.gn to load the correct V8 snapshot configuration

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index f1583abaf03c6b8298af5d36c099f03c7bbf1e36..3b029b5fb0a7417f728982a66e54cec1e45880fe 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -2,6 +2,7 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build_overrides/v8.gni")
 import("//testing/test.gni")
 import("pdfium.gni")
 
@@ -170,6 +171,7 @@ source_set("test_support") {
       "//v8",
       "//v8/include",
     ]
+    configs += [ "//v8:external_startup_data" ]
   }
   configs += [ ":pdfium_config" ]
 }
@@ -688,6 +690,7 @@ static_library("javascript") {
     public_deps = [
       "//v8",
     ]
+    configs += [ "//v8:external_startup_data" ]
   } else {
     sources += [ "fpdfsdk/src/javascript/JS_Runtime_Stub.cpp" ]
   }
@@ -780,6 +783,7 @@ test("pdfium_embeddertests") {
       "//v8",
       "//v8/include",
     ]
+    configs += [ "//v8:external_startup_data" ]
   }
   configs += [ ":pdfium_config" ]
 }