correctly handle Tcl stub library if available

tools/swig/CMakeLists.txt

@@ -94,6 +94,11 @@ if(BUILD_SWIG_TCL)
   if(NOT TCL_FOUND)
     message(FATAL_ERROR "Tcl development headers and libraries are required")
   endif()
+  find_package(TclStub)
+  if(TCL_STUB_LIBRARY)
+    target_compile_definitions(tcllammps PRIVATE USE_TCL_STUBS)
+    target_link_libraries(tcllammps PRIVATE ${TCL_STUB_LIBRARY})
+  endif()
   target_include_directories(tcllammps PRIVATE ${TCL_INCLUDE_PATH})
   swig_link_libraries(tcllammps PRIVATE lammps ${TCL_LIBRARY})
   # build extended Tcl shell binary