Provide fake definitions for libstdc++.

libstdc++ needs to be able to `using ::foo` these in the various C++
wrapper headers for the C library. The NDK long ago added fake
definitions. We need to keep the same.

Test: make checkbuild
Bug: http://b/30465923
Change-Id: Id513b72a59eafcc823080631e07b21290d5e3b24