GN: Build with a custom libc++ when using ASAN, TSAN or MSAN.

build/config/sanitizers/BUILD.gn

 # Copyright 2014 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/sanitizers/sanitizers.gni")
+
 # Contains the dependencies needed for sanitizers to link into executables and
 # shared_libraries. Unconditionally depend upon this target as it is empty if
-# |is_asan|, |is_lsan|, |is_tsan| and |is_msan| are false.
+# |is_asan|, |is_lsan|, |is_tsan|, |is_msan| and |use_custom_libcxx| are false.
 group("deps") {
+  deps = []
   if (is_asan || is_lsan || is_tsan || is_msan) {
     public_configs = [ ":sanitizer_options_link_helper" ]
-    deps = [
-      ":options_sources",
-    ]
+    deps += [ ":options_sources" ]
+  }
+  if (use_custom_libcxx) {
+    deps += [ "//buildtools/third_party/libc++:libcxx_proxy" ]
   }
 }
 
 config("sanitizer_options_link_helper") {
   ldflags = [ "-Wl,-u_sanitizer_options_link_helper" ]
   if (is_asan) {
     ldflags += [ "-fsanitize=address" ]
   }
   if (is_lsan) {
     ldflags += [ "-fsanitize=leak" ]
@@ skipping 20 matching lines @@
   }
 
   if (is_lsan) {
     sources += [ "//build/sanitizers/lsan_suppressions.cc" ]
   }
 
   if (is_tsan) {
     sources += [ "//build/sanitizers/tsan_suppressions.cc" ]
   }
 }