Summary:
Now that the fb-mercurial sources are available in the Eden repository, update
our CMake build files to always build them. This moves the build logic from
the centralized `FBMercurialFeatures.cmake` file into `CMakeLists.txt` files
in the appropriate subdirectories.
Reviewed By: chadaustin
Differential Revision: D18588011
fbshipit-source-id: ded9decde5c2ec766aae0bb0f4f5b021d1044a98
Summary:
In preparation for merging fb-mercurial sources to the Eden repository,
move everything from the top-level directory into an `eden/scm`
subdirectory.