udpipe: [OS X] pip install, fatal error: 'atomic' file not found

I just tried to install this using pip install ufal.udpipe, but I got the following error:

    building 'ufal_udpipe' extension
    creating build/temp.macosx-10.6-x86_64-3.5
    creating build/temp.macosx-10.6-x86_64-3.5/udpipe
    /usr/bin/clang -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I/Applications/anaconda/include -arch x86_64 -Iudpipe/include -I/Applications/anaconda/include/python3.5m -c udpipe/udpipe.cpp -o build/temp.macosx-10.6-x86_64-3.5/udpipe/udpipe.o -std=c++11 -fvisibility=hidden -w
    udpipe/udpipe.cpp:7:10: fatal error: 'atomic' file not found
    #include <atomic>
             ^
    1 error generated.
    error: command '/usr/bin/clang' failed with exit status 1

    ----------------------------------------
Command "/Applications/anaconda/bin/python -u -c "import setuptools, tokenize;__file__='/private/tmp/pip-build-qx1s775a/ufal.udpipe/setup.py';exec(compile(getattr(tokenize, 'open', open)(__file__).read().replace('\r\n', '\n'), __file__, 'exec'))" install --record /tmp/pip-03jnjoj8-record/install-record.txt --single-version-externally-managed --compile" failed with error code 1 in /private/tmp/pip-build-qx1s775a/ufal.udpipe/

Stack Overflow suggests that this is due to a flag in the compiler. But I do not know how to fix this using pip.