gn: define and use clang_base_path

build/config/clang/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("clang.gni")
 import("//build/config/chromecast_build.gni")
 
 config("find_bad_constructs") {
   if (clang_use_chrome_plugins) {
     cflags = []
 
     # On Windows, the plugin is built directly into clang, so there's
     # no need to load it dynamically.
 
     if (is_mac || is_ios) {
       cflags += [
         "-Xclang",
         "-load",
         "-Xclang",
-        rebase_path(
-            "//third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.dylib",
-            root_build_dir),
+        rebase_path("${clang_base_path}/lib/libFindBadConstructs.dylib",
+                    root_build_dir),
       ]
     } else if (is_linux || is_android) {
       cflags += [
         "-Xclang",
         "-load",
         "-Xclang",
-        rebase_path(
-            "//third_party/llvm-build/Release+Asserts/lib/libFindBadConstructs.so",
-            root_build_dir),
+        rebase_path("${clang_base_path}/lib/libFindBadConstructs.so",
+                    root_build_dir),
       ]
     }
 
     cflags += [
       "-Xclang",
       "-add-plugin",
       "-Xclang",
       "find-bad-constructs",
       "-Xclang",
       "-plugin-arg-find-bad-constructs",
@@ skipping 23 matching lines @@
 # Enables some extra Clang-specific warnings. Some third-party code won't
 # compile with these so may want to remove this config.
 config("extra_warnings") {
   cflags = [
     "-Wheader-hygiene",
 
     # Warns when a const char[] is converted to bool.
     "-Wstring-conversion",
   ]
 }