Add GN targets for libc++ and libc++abi.

third_party/libc++/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.
+
+shared_library("libc++") {
+  sources = [
+    "trunk/src/algorithm.cpp",
+    "trunk/src/bind.cpp",
+    "trunk/src/chrono.cpp",
+    "trunk/src/condition_variable.cpp",
+    "trunk/src/debug.cpp",
+    "trunk/src/exception.cpp",
+    "trunk/src/future.cpp",
+    "trunk/src/hash.cpp",
+    "trunk/src/ios.cpp",
+    "trunk/src/iostream.cpp",
+    "trunk/src/locale.cpp",
+    "trunk/src/memory.cpp",
+    "trunk/src/mutex.cpp",
+    "trunk/src/new.cpp",
+    "trunk/src/optional.cpp",
+    "trunk/src/random.cpp",
+    "trunk/src/regex.cpp",
+    "trunk/src/shared_mutex.cpp",
+    "trunk/src/stdexcept.cpp",
+    "trunk/src/string.cpp",
+    "trunk/src/strstream.cpp",
+    "trunk/src/system_error.cpp",
+    "trunk/src/thread.cpp",
+    "trunk/src/typeinfo.cpp",
+    "trunk/src/utility.cpp",
+    "trunk/src/valarray.cpp",
+  ]
+  configs -= [
+    "//build/config/compiler:chromium_code",
+    "//build/config/compiler:no_rtti",
+    "//build/config/gcc:no_exceptions",
+    "//build/config/gcc:symbol_visibility_hidden",
+  ]
+  configs += [
+    "//build/config/compiler:no_chromium_code",
+    "//build/config/compiler:rtti",
+    "//build/config/sanitizers:sanitizer_options_link_helper",
+    "//buildtools/third_party/libc++abi:config",
+  ]
+
+  # libc++abi is linked statically into libc++.so. This allows us to get both
+  # libc++ and libc++abi by passing '-stdlib=libc++'. If libc++abi was a
+  # separate DSO, we'd have to link against it explicitly.
+  deps = [
+    "//buildtools/third_party/libc++abi",
+  ]
+}
+
+group("libcxx_proxy") {
+  deps = [
+    ":libc++",
+  ]
+  public_configs = [ ":link_helper" ]
+}
+
+config("link_helper") {
+  ldflags = [
+    "-stdlib=libc++",
+
+    # Normally the generator takes care of RPATH. Our case is special because
+    # the generator is unaware of the libc++.so dependency. Note that setting
+    # RPATH here is a potential security issue. See the following for another
+    # example of this issue: https://code.google.com/p/gyp/issues/detail?id=315
+    "-Wl,-R,\$ORIGIN/",

[earthdok, 2015/05/26 16:18:46]

$ORIGIN/lib?

[Sam McNally, 2015/05/27 00:12:09]

GN puts shared libraries in out/Foo instead of out/Foo/lib.

+  ]
+  lib_dirs = [ root_build_dir ]
+}