Android 32-bit compilation broken for standalone toolchain with unified headers

Using a standalone toolchain built from NDK-r14b using --arch arm --api 21 --stl libc++ --unified-headers and a toolchain file that makes use of CMakes Android platform support, compilation is broken.

Specifically, cmath reports a number of undefined symbols including abs, isdigit, and several others due to the order of the system search paths being incorrect. ${SYSROOT}/usr/include must come after ${TOOLCHAIN}/include/c++/...

The offending line appears to be Android-Common.cmake:159, where it adds ${CMAKE_SYSROOT}/usr/include to CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES. Removing this line resolves the problem, as does preemptively setting CMAKE_CXX_STANDARD_INCLUDE_DIRECTORIES to ${CMAKE_SYSROOT}/include/c++/4.9.0