added -Wno-c++11-long-long flag for clang++ in linux. Fixes issue #62
added -Wno-c++11-long-long flag for clang++ in mac
Change ordering of Wno-c++11-long-long to ensure it is respected.
Merge pull request #117 from stan-dev/feature/issue62

added -Wno-c++11-long-long flag for clang++ in linux. Fixes #62.