Cython build can't find C++11 STL files - but only when called from setup.py

When I compile my code from setup.py, it can't find the C++11 include file <array> - but C++11 compiler features do work.

When I paste the same command line that setup.py generates into my shell, it all compiles perfectly well(!)

Code demonstrating this behavior can be seen here and is also pasted below.

---

Terminal session:

$ python setup.py build_ext
running build_ext
building 'simple' extension
creating build
creating build/temp.macosx-10.6-intel-3.4
/usr/bin/clang -fno-strict-aliasing -Werror=declaration-after-statement -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -arch i386 -arch x86_64 -g -Isrc -I/Library/Frameworks/Python.framework/Versions/3.4/include/python3.4m -c simple.cpp -o build/temp.macosx-10.6-intel-3.4/simple.o -Wno-unused-function -std=c++11
In file included from simple.cpp:289:
./simple.h:2:10: fatal error: 'array' file not found
#include <array>
         ^
1 error generated.
error: command '/usr/bin/clang' failed with exit status 1

$ /usr/bin/clang -fno-strict-aliasing -Werror=declaration-after-statement -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -arch i386 -arch x86_64 -g -Isrc -I/Library/Frameworks/Python.framework/Versions/3.4/include/python3.4m -c simple.cpp -o build/temp.macosx-10.6-intel-3.4/simple.o -Wno-unused-function -std=c++11

# no error!

$  /usr/bin/clang --version
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.4.0
Thread model: posix

---

setup.py:

#!/usr/bin/env python3

import platform, distutils.core, distutils.extension, Cython.Build

EXTENSION = distutils.extension.Extension(
    name='simple',
    sources=['simple.pyx'],
    extra_compile_args=['-Wno-unused-function', '-std=c++11'],
    language='c++',
    )

EXT_MODULES=Cython.Build.cythonize(
    [EXTENSION],
    language='c++',
    )

distutils.core.setup(
    name='simple',
    ext_modules=EXT_MODULES,
    )

---

simple.pyx:

cdef extern from "simple.h" namespace "fcolor4":
    struct Simple:
        int x

---

simple.h:

int foo() {
    auto x = 1;   // works, so must be C++11
    return x;
}

#include <string>  // works, so must find some STL.
#include <array>   // fails!