Add support for the Windows ASan configuration to the gn build

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/compiler/compiler.gni")
 import("//build/config/sanitizers/sanitizers.gni")
 import("//build/config/win/visual_studio_version.gni")
 
 assert(is_win)
 
@@ skipping 68 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/3.9.0/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" ]
   }
 }
 
 config("vs_code_analysis") {
@@ skipping 275 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" ]
   }
 }