* Build LLVM at CMake config time and use CMake config file for dependencies.

* Temp save.

* Codegen functioning.

* Support prebuilt LLVM.

* Remove zlib.

* Relax CMake minimum version.

* Fix bug.

* Lower CMake version requirement.

* Pass more args.

* Add proper quote.

* Remove quotes.

* Try to separate flags for external projects.

* Don't pass flags to LLVM.

* Pass CXX abi.

* Remove stale print.

* Update gtest flags.

* Try to fix build issue.

* Patch LLVM to prevent building clang-tools-extra.
Co-authored-by: aslepko <44713115+aslepko@users.noreply.github.com>

* Update license to new year

* Pick up some strays

* Cleanup how compile flags set and used by nGraph and external projects.
Set C++11 through CMake and pass it down to external projects.
Prefer CMake variables such as CMAKE_POSITION_INDEPENDENT_CODE and
CMAKE_CXX_STANDARD instead of explicitly setting compiler dependent
flags.
Create json compilation database for external projects.
CMAKE_CXX_FLAGS is used as common global options for nGraph and external
projects.
add_compile_options() is used for local options for current and sub
directories.
add_definitions() is used for setting definitions for current and sub
directories.
Note: Global options are not passed down to some external projects.
Note: mkl-dnn resets CMAKE_CXX_FLAGS internally.
Note: TBB and MLSL are not CMake based.
Noet: Eigen and json is header only library.

* Fix error.

* Fix error. (second attempt)

* Cleanup code.

* Allow check for undefined macro.

* Try to fix cldnn issue.

* Set type for CMake arguments.

* Pass C++ standard to protobuf.

* Pass C++ standard down to TBB.

* Change how Clang specific flags are handled.

* Fix error.

* Workaround for compile error on Baidu's PDPD docker.

* Fix windows build error.

* update licenses for 2019

* style

* more sdl changes

* more fixes

* update SDL

* cleanup

* cleanup

* rename var

* redo how in_transition is handled

* add -O2 flag back