Adding MPI back to Boost

[Sean Farley]

Ryan Schmidt writes:

> On Dec 14, 2014, at 2:28 AM, Sean Farley wrote:
>
>> So, I've added support into the compilers portgroup for working with
>> the compiler.blacklist variable but that doesn't fix the issue that Ryan
>> tried to fix with r125939:
>> 
>> https://trac.macports.org/changeset/125939
>> 
>> It seems instead that the fix is just to remove the gcc variants:
>> 
>> mpi.setup -gcc
>> 
>> Is there anything wrong with this proposed fix? If no one objects, I'll
>> push my changesets which 1) add blacklist support to the compilers
>> portgroup and 2) add mpi portgroup to boost (but remove gcc variants).
>
> Right, using gcc variants causes the use of libstdc++ which causes the problem on Mavericks and later.
>
> So, without gcc variants, what variants remain?

clang 3.x and all versions of dragonegg. Multiple that set with all the
mpi choices, too.