Suppress compiler and linker warnings in v8 test binaries

test/unittests/BUILD.gn

 # Copyright 2016 The V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # Please keep this file in sync with unittests.gyp.
 
 import("../../gni/v8.gni")
 
 executable("unittests") {
   testonly = true
@@ skipping 147 matching lines @@
     "//testing/gtest",
   ]
 
   if (is_component_build) {
     # compiler-unittests can't be built against a shared library, so we
     # need to depend on the underlying static target in that case.
     deps += [ "../..:v8_maybe_snapshot" ]
   } else {
     deps += [ "../..:v8" ]
   }
+
+  if (is_win) {
+    # This warning is benignly triggered by the U16 and U32 macros in
+    # bytecode-utils.h.
+    # C4309: 'static_cast': truncation of constant value
+    cflags = [ "/wd4309" ]
+
+    # Suppress warnings about importing locally defined symbols.
+    if (is_component_build) {
+      ldflags = [ "/ignore:4049", "/ignore:4217" ]
+    }
+  }
 }