Building shared library has been broken after 82e2ac1 / D91009064

[cho-m]

This was seen in Homebrew where we provide shared libraries for various weekly tagged Facebook projects.

The build seems to have been broken by the CMake refactoring in 82e2ac1 / D91009064. No issues in mvfst,
fizz, and wangle so the granular CMake targets work there for shared libraries.

---

Specifically, when attempting a build with -DBUILD_SHARED_LIBS=ON for latest v2026.03.02.00, CMake errors with

CMake Error at proxygen/lib/CMakeLists.txt:117 (target_include_directories):
  target_include_directories may only set INTERFACE properties on INTERFACE
  targets


CMake Error at proxygen/lib/CMakeLists.txt:131 (target_include_directories):
  target_include_directories may only set INTERFACE properties on INTERFACE
  targets


-- Configuring incomplete, errors occurred!

After trying a local fix for above, CMake fails on a new issue for cycle in dependency graph:

CMake Error: The inter-target dependency graph contains the following strongly connected component (cycle):
  "proxygen" of type SHARED_LIBRARY
    depends on "proxygen_http_http_message_filters_obj" (strong)
    depends on "proxygen_http_client_obj" (strong)
    depends on "proxygen_http_http_connector_with_fizz_obj" (strong)
    depends on "proxygen_http_hq_connector_obj" (strong)
    depends on "proxygen_http_codec_util_obj" (strong)
    depends on "proxygen_http_codec_codec_common_obj" (strong)
    depends on "proxygen_http_codec_http1x_codec_obj" (strong)

...

  "proxygen_hq_server_obj" of type OBJECT_LIBRARY
    depends on "proxygen_http_session_hq_session_obj" (weak)
    depends on "proxygen_http_codec_codec_common_obj" (weak)
    depends on "proxygen" (weak)
    depends on "proxygen_http_codec_compress_hpack_obj" (weak)
    depends on "proxygen_http_codec_util_obj" (weak)

...

    depends on "proxygen_http_session_server_obj" (weak)
    depends on "proxygen_http_codec_codec_factory_obj" (weak)
    depends on "proxygen_http_session_http_session_codec_factory_obj" (weak)
    depends on "proxygen_http_session_hq_downstream_session_obj" (weak)
At least one of these targets is not a STATIC_LIBRARY.  Cyclic dependencies are allowed only among static libraries.
CMake Generate step failed.  Build files cannot be regenerated correctly.

So the changes may only work for static library.