tr1 no longer needed since we do compile with c++11 support

Looks like the clang shipped with the ndk is missing the __atomic_load intrinsic so that we get a link error if not using stuff from boost:

/opt/google/android-ndk-r9/sources/cxx-stl/gnu-libstdc++/4.8/include/bits/shared_ptr_base.h:194: error: undefined reference to '__atomic_load'

So I fail-over the GNU toolchain.