fbcode_builder: cmake: propagate thrift include dependencies correctly
fbcode_builder: cmake: propagate thrift include dependencies correctly

Summary:
Update `add_thrift_cpp2_library()` to pass in the correct `-I` flags when
invoking the thrift compiler so that it can find all of the other thrift files
that this library depends on.

D16062657 was a previous attempt to do this, but suffered from a few problems:
- It required all dependencies to be defined before
  `add_thrift_cpp2_library()` was called.  This requires users to carefully
  order their CMake files and subdirectory include ordering.
- It only handled one level of dependencies, and did not propagate include
  paths for deeper dependencies.
- It set the include path for dependencies to the source directory path where
  the dependency was originally built, rather than the directory where the
  thrift file for that dependency would be installed.

This change does require CMake 3.8+.  Previous versions of CMake do not
support using generator expressions to generate multiple arguments for a
custom command.

Reviewed By: strager

Differential Revision: D17005381

fbshipit-source-id: 31190beba94b4d1010445375a5e2791450230f7d

facebook/wangle,facebook/wangle,facebook/wangle