Link the OpenMP runtime used by system OpenSubdiv.
--- a/build_files/cmake/Modules/FindOpenSubdiv.cmake
+++ b/build_files/cmake/Modules/FindOpenSubdiv.cmake
@@ -56,6 +56,11 @@
   list(APPEND _opensubdiv_LIBRARIES "${OPENSUBDIV_${UPPERCOMPONENT}_LIBRARY}")
 endforeach()
 
+find_package(OpenMP QUIET)
+if(OpenMP_CXX_FOUND)
+  list(APPEND _opensubdiv_LIBRARIES OpenMP::OpenMP_CXX)
+endif()
+
 # Return values:
 # - `${variable_name}`: `TRUE` if the controller include file exists.
 function(OPENSUBDIV_CHECK_CONTROLLER