Force libc++ on macOS

[jakirkham]

Some Python builds still try to use stdlibc++, which really doesn't exist on macOS any more. So force libc++ to bypass this issue.

Note: Hopefully addresses the macOS part of issue ( #210 ).

TODO:

• Unit tests and/or doctests in docstrings
• tox -e py38 passes locally
• tox -e py27 passes locally
• Docstrings and API docs for any new/modified user-facing classes and functions
• Changes documented in docs/release.rst
• tox -e docs passes locally
• AppVeyor and Travis CI passes
• Test coverage to 100% (Coveralls passes)

[jakirkham]

@jni, would you be able to try this out and let me know if it helps the macOS build situation? 🙂

[jni]

How do I build from source? If I try pip install -U . on your branch, I get:

    creating build/temp.macosx-10.7-x86_64-3.7
    creating build/temp.macosx-10.7-x86_64-3.7/numcodecs
    gcc -Wno-unused-result -Wsign-compare -Wunreachable-code -DNDEBUG -g -fwrapv -O3 -Wall -Wstrict-prototypes -I/Users/nuneziglesiasj/conda/envs/napari-numcodecs/include -arch x86_64 -I/Users/nuneziglesiasj/conda/envs/napari-numcodecs/include -arch x86_64 -DHAVE_LZ4=1 -DHAVE_SNAPPY=1 -DHAVE_ZLIB=1 -DHAVE_ZSTD=1 -Ic-blosc/blosc -I/Users/nuneziglesiasj/conda/envs/napari-numcodecs/include/python3.7m -c numcodecs/blosc.c -o build/temp.macosx-10.7-x86_64-3.7/numcodecs/blosc.o -msse2 -stdlib=libc++ -DSHUFFLE_SSE2_ENABLED
    numcodecs/blosc.c:705:10: fatal error: 'blosc.h' file not found
    #include "blosc.h"
             ^~~~~~~~~

[jakirkham]

There's a git submodule for Blosc. So you would need to run git submodule update --init to grab that.

[jni]

Ok, it's working now! 🎉

[jakirkham]

That's great news! Thanks for testing and bearing with me. 😅

[jni]

Least I can do! 😅