Fix boost 1.55 compile errors

This gets boost 1.55 to compile on Mac OSX via superbuild.
This is tested against 10.9 and Clang 5.1

The two patches are required when compiling with clang 5.1.
https://github.com/Homebrew/homebrew/commit/a20650deb61faa38356b370bcbaa
f35c195135b4

In the future the -stdlib=libstdc++ should be removed since libc++ is the default stdlib in 10.9. All Macs back to 10.7 have libc++ on them, however, libstdc++ is the default on those older versions of OSX. If in the future Openstudio wants to use c++11 features, libc++ will have to be used on Mac.

@macumber