Cherry-pick libc++ bug fixes. This fixes the stack trace issue when compiling Android chromium with libc++. BUG=490275 Change-Id: Ifc12b502535a2c53129f89f6bb5dde2c376ce7c7 Reviewed-on: https://chromium-review.googlesource.com/287200 Reviewed-by: Ross McIlroy <rmcilroy@chromium.org> Tested-by: Ross McIlroy <rmcilroy@chromium.org>