OpenSubdiv's CPU backend may be built with OpenMP (and built by default).
Unfortunately, OSD does not fill OpenMP in INTERFACE_LINK_LIBRARIES,
causing __kmpc_fork_call link failures when built with Clang.
--- a/build_files/cmake/Modules/FindOpenSubdiv.cmake
+++ b/build_files/cmake/Modules/FindOpenSubdiv.cmake
@@ -56,6 +56,11 @@ foreach(COMPONENT ${_opensubdiv_FIND_COMPONENTS})
   list(APPEND _opensubdiv_LIBRARIES "${OPENSUBDIV_${UPPERCOMPONENT}_LIBRARY}")
 endforeach()
 
+find_package(OpenMP QUIET)
+if(OpenMP_CXX_FOUND)
+  list(APPEND _opensubdiv_LIBRARIES OpenMP::OpenMP_CXX)
+endif()
+
 macro(OPENSUBDIV_CHECK_CONTROLLER
       controller_include_file
       variable_name)