Untangle third party inclusion in CMake (#3457)

Summary: Pull Request resolved: https://github.com/pytorch/audio/pull/3457

Differential Revision: D47241343

Pulled By: mthrok

fbshipit-source-id: fd1bfd1531397cb59e9cf11de9dede6949f8517e

CMakeLists.txt

@@ -165,9 +165,9 @@ else()
   message(STATUS "Could not find ccache. Consider installing ccache to speed up compilation.")
 endif()
 
-add_subdirectory(third_party)
 add_subdirectory(torchaudio/csrc)
 if (BUILD_SOX)
+  add_subdirectory(third_party/sox)
   add_subdirectory(torchaudio/csrc/sox)
 endif()
 if (USE_FFMPEG)

third_party/CMakeLists.txt

-set(CMAKE_CXX_VISIBILITY_PRESET hidden)
-
-file(MAKE_DIRECTORY install/include)
-file(MAKE_DIRECTORY install/lib)
-
-################################################################################
-# sox
-################################################################################
-if (BUILD_SOX)
-  add_subdirectory(sox)
-endif()