Adding support for building on OS X

[poulson]

In addition to creating a new profile, sandybridge_osx_clang, I have finished working around the missing pthread_barrier functionality and generalized the build system to support more general shared and static library suffixes (e.g., .dylib for shared libraries on OS X). Lastly, I enabled shared-library builds by default in each of the configurations.

[jeffhammond]

This looks good to me but I have not tested.

@fgvanzee Would you like me test locally? I recall you may be a "serious programmer" (Linux laptop person).

[Maratyszcza]

Is the new osx configuration only due to BLIS_ENABLE_PTHREADS vs BLIS_ENABLE_OPENMP?

[poulson]

@Maratyszcza I believe that was the only change I made to bli_config.h (most changes were elsewhere)

[Maratyszcza]

@fgvanzee Maybe multithreading model should be an argument to ./configure instead of an option in configuration file? After all, it is not specific to CPU microarchitecture

[poulson]

@Maratyszcza Agreed; in this case, it's a matter of compiler support.

[jeffhammond]

Is this still an issue? I can't cleanly merge this PR with the latest master and I wonder if it needs to be sorted out or not.

[devinamatthews]

Is the only issue that it doesn't work "out of the box" with Apple's version of gcc/llvm (due do missing pthread_barrier)? If so we have a non-pthread barrier already that could be hooked up easily. The so/dyld stuff could be helpful but the linker manages to figure out what you mean with .so as far as I can tell. I don't think the sandybridge_osx_clang configuration stuff is necessary with various new configure options.

On the other hand, if we are fine not supporting Apple's gimped compilers then I think there is nothing to do at this point.

[jeffhammond]

It is worth adding the workaround for missing pthread_barrier since that is not POSIX anyways.

[devinamatthews]

@tlrmchlsmth I think you have the skillz to pay the billz on this one.

[tlrmchlsmth]

Actually I already fixed the pthread barrier thing but I didn't know this issue was here.
The default right now is to not use pthread barriers, and if you want to use them, you have to define BLIS_USE_PTHREAD_BARRIER.

[jeffhammond]

I guess it can be resolved although it's good to setup Mac builds in Travis
to validate this and other changes.

If Mac is tested in Travis already, I apologize. I'm not using a client
that makes checking that trivial.

Jeff Hammond
jeff.science@gmail.com
http://jeffhammond.github.io/

[devinamatthews]

Obsoleted by #108.