Enable C++11 on posix.

Since building with msvc12 on Windows now, support for C++11 is already enabled there implicitly.

This set of commits enables it for Linux and Mac. I tested with the Clang 3.4 on our Linux build VM.

-Wno-deprecated-register is added since the "register" keyword used in some of the SDKs is deprecated in C++11.

-Wno-implicit-exception-spec-mismatch is added for our delete and delete[] overrides.
Without it, when building with C++ enabled, the warning is thrown (at least on linux with gcc 4.7 C++ headers) due to those functions being defined in the headers with _GLIBCXX_USE_NOEXCEPT. I don't know how portable that is - if we can just add it to our versions if __linux__ is defined so I silenced the warning/error. We can always adjust things later if necessary.