Numpy 1.11 doesn't install in virtualenv @ Ubuntu Studio
There exists pre-built binary package for your platform, you should be able install it via wheel:
pip install wheel
pip install numpy==1.11.*
If you have some reasons to build the package from source instead, according to this commit, I think it's better to
ln -s /usr/include/x86_64-linux-gnu/bits/types/__locale_t.h /usr/include/xlocale.h