C++11 requirements for CMake need tweaking

[jefftrull]

Per @pdimov 's post on boost-devel, there are a few requirements for CMake that I didn't update correctly when we began requiring C++11. In particular:

• cmake_minimum_required needs to be at least 3.8
• there is no target_compile_features specifying C++11
• the dependency on Boost.format is not reflected

Generally speaking, the CMake build flow is a parallel one that needs to be maintained as we change the bjam stuff.

[pdimov]

You can just rerun boostdep --cmake wave, but the output isn't 100% correct because you need two more source files

  src/cpplexer/re2clex/aq.cpp
  src/cpplexer/re2clex/cpp_re.cpp

that boostdep doesn't pick up because they're in a subdirectory.