lib-ified core cpp11-migrate functionality to support unit tests

Summary:
Transform.* and Transforms.* moved to form a new library: libmigrateCore.
#includes updated to point to new header locations.

To support autoconf build, Cpp11Migrate.cpp moved to new subdirectory 'tool'
which also contains build files for creating final binary.

CMake and autoconf updated to build the new library and link it with
cpp11-migrate and with cpp11-migrate unit tests.

Dummy unit tests replaced with simple, but real, tests for Transform's public
interface.

TODO: Lib-ifying the transforms to further simplify build of cpp11-migrate.
llvm-svn: 178785