Add gn Blink GC plugin options

build/config/posix/BUILD.gn

 # Copyright 2015 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/sanitizers/sanitizers.gni")
 import("//build/config/sysroot.gni")
 import("//build/toolchain/toolchain.gni")
 
 assert(is_posix)
 
 group("posix") {
   visibility = [ "//:optimize_gn_gen" ]
 }
 
 # This is included by reference in the //build/config/compiler config that
 # is applied to all Posix targets. It is here to separate out the logic that is
 # Posix-only. Note that this is in addition to an OS-specific variant of this
 # config.
 config("compiler") {
   if ((allow_posix_link_time_opt || is_cfi) && !is_nacl) {
     arflags = [
       "--plugin",
-      rebase_path("//third_party/llvm-build/Release+Asserts/lib/LLVMgold.so",
-                  root_build_dir),
+      rebase_path("$clang_base_path/lib/LLVMgold.so", root_build_dir),
     ]
   }
 }
 
 # This is included by reference in the //build/config/compiler:runtime_library
 # config that is applied to all targets. It is here to separate out the logic
 # that is Posix-only. Please see that target for advice on what should go in
 # :runtime_library vs. :compiler.
 config("runtime_library") {
   if (!is_mac && !is_ios && sysroot != "") {
     # Pass the sysroot to all C compiler variants, the assembler, and linker.
     cflags = [ "--sysroot=" + rebase_path(sysroot, root_build_dir) ]
     asmflags = cflags
     ldflags = cflags
 
     # Need to get some linker flags out of the sysroot.
     ldflags += exec_script("sysroot_ld_path.py",
                            [
                              rebase_path("//build/linux/sysroot_ld_path.sh",
                                          root_build_dir),
                              rebase_path(sysroot),
                            ],
                            "list lines")
   }
 }