Add gn Blink GC plugin options

build/config/win/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+import("//build/config/clang/clang.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/win/visual_studio_version.gni")
 import("//build/toolchain/toolchain.gni")
 
 assert(is_win)
 
 declare_args() {
   # Set this to true to enable static analysis through Visual Studio's
   # /analyze. This dramatically slows compiles and reports thousands of
@@ skipping 71 matching lines @@
     if (exec_script("//build/win/use_ansi_codes.py", [], "trim string") ==
         "True") {
       cflags += [
         # cmd.exe doesn't understand ANSI escape codes by default,
         # so only enable them if something emulating them is around.
         "-fansi-escape-codes",
       ]
     }
 
     # Clang runtime libraries, such as the sanitizer runtimes, live here.
-    lib_dirs = [ "//third_party/llvm-build/Release+Asserts/lib/clang/$clang_version/lib/windows" ]
+    lib_dirs = [ "$clang_base_path/lib/clang/$clang_version/lib/windows" ]
   }
 
   if (is_syzyasan) {
     # SyzyAsan needs /PROFILE turned on to produce appropriate pdbs.
     assert(!is_win_fastlink, "/PROFILE and /DEBUG:FASTLINK are incompatible")
     ldflags = [ "/PROFILE" ]
   }
 
   # arflags apply only to static_libraries. The normal linker configs are only
   # set for executable and shared library targets so arflags must be set
@@ skipping 279 matching lines @@
 
 # Internal stuff --------------------------------------------------------------
 
 # Config used by the MIDL template to disable warnings.
 config("midl_warnings") {
   if (is_clang) {
     # MIDL generates code like "#endif !_MIDL_USE_GUIDDEF_".
     cflags = [ "-Wno-extra-tokens" ]
   }
 }