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

third_party/libc++abi/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.
+
+config("config") {

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

If you want to have a common config then please move it to libc++/BUILD.gn.

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

Done.

+  include_dirs = [
+    "trunk/include",

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

What is this path relative to? I.e., when libc++/BUILD.gn includes this config,
will "trunk/include" evaluate to "libc++abi/trunk/include" or
"libc++/trunk/include"?

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

Relative to the BUILD.gn containing the config. While the config was in this
file "trunk/include" would always evaluate to "libc++abi/trunk/include", no
matter what depends on the config.

+    "../libc++/trunk/include",
+  ]
+  cflags = [
+    "-fstrict-aliasing",
+    "-nostdinc++",
+    "-std=c++11",
+  ]
+  ldflags = [ "-nodefaultlibs" ]
+
+  # TODO(GYP): Remove "-pthread" from ldflags. It somehow causes a warning from
+  # clang about an unused compilation option.
+  # TODO(earthdok): find out what's causing the warning.

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

I'm resolving this TODO in https://codereview.chromium.org/1154213002/ It also
contains a few minor flag changes.

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

Done.

+  libs = [
+    "c",
+    "gcc_s",
+    "pthread",
+    "rt",
+  ]
+}
+
+static_library("libc++abi") {
+  sources = [
+    "trunk/src/abort_message.cpp",
+    "trunk/src/cxa_aux_runtime.cpp",
+    "trunk/src/cxa_default_handlers.cpp",
+    "trunk/src/cxa_demangle.cpp",
+    "trunk/src/cxa_exception.cpp",
+    "trunk/src/cxa_exception_storage.cpp",
+    "trunk/src/cxa_guard.cpp",
+    "trunk/src/cxa_handlers.cpp",
+    "trunk/src/cxa_new_delete.cpp",
+    "trunk/src/cxa_personality.cpp",
+    "trunk/src/cxa_unexpected.cpp",
+    "trunk/src/cxa_vector.cpp",
+    "trunk/src/cxa_virtual.cpp",
+    "trunk/src/exception.cpp",
+    "trunk/src/private_typeinfo.cpp",
+    "trunk/src/stdexcept.cpp",
+    "trunk/src/typeinfo.cpp",
+  ]
+  configs -= [
+    "//build/config/compiler:chromium_code",
+    "//build/config/compiler:no_rtti",
+    "//build/config/gcc:no_exceptions",
+    "//build/config/gcc:symbol_visibility_hidden",
+  ]
+  configs += [
+    ":config",
+    "//build/config/compiler:no_chromium_code",
+    "//build/config/compiler:rtti",
+  ]
+}