- Use cmake_dependent_option() for all threading models and encode their
respective mutual exclusivity in the dependent-option s/t the job of
ensuring mutual exclusivity is performed by CMake.
- Use of cmake_dependent_option() has the downside that options are
removed from the GUI if their requirements for availability are not
met. So if CXX11 is OFF, then neither TBB nor CXX11_THREADS will
even appear as options (they will be undefined, assumed OFF).
- Perform checks for availability of C++11 if CXX11 is enabled prior to
testing other options to handle dependence of TBB & CXX11_THREADS on
CXX11 actually being present.
- Add check for availability of C++11-specific math functions used in
jet.h before reporting C++11 as found.
- Add check for <atomic> before allowing TBB or CXX11_THREADS, as both
options require it and it may not always be available even if the
other required C++11 components are.
Change-Id: Ife8cd182aeb1978539ce2c9966910ae59ebd9177
Alex Stewart