[Chromecast] Include all stdlibc++/libgcc symbols in cast_shell.

build/config/chromecast/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.
+
+assert(is_chromecast)
+
+config("static_config") {
+  ldflags = [
+    # We want to statically link libstdc++/libgcc.
+    "-static-libstdc++",
+    "-static-libgcc",
+  ]
+}
+
+config("executable_config") {
+  ldflags = [
+    "-lm",  # stdlibc++ requires math.h
+
+    # Export the libstdc++ symbols so multiple copies merge at runtime.
+    "-Wl,--export-dynamic",
+
+    # In case we redefined stdlibc++ symbols (e.g. tc_malloc)
+    "-Wl,--allow-multiple-definition",
+
+    "-Wl,--whole-archive",
+    "-l:libstdc++.a",
+    "-l:libgcc.a",
+    "-Wl,--no-whole-archive",
+  ]
+
+  configs = [ ":static_config" ]
+}
+
+config("shlib_config") {
+  configs = [ ":static_config" ]
+}