core/imt: link privately to libThread and TBB

This is to avoid direct linking to TBB in e.g. libTree,
since TBB should be encapsulated by libImt.

core/imt/CMakeLists.txt

@@ -5,16 +5,15 @@
 ROOT_LINKER_LIBRARY(Imt
     src/base.cxx
     src/TTaskGroup.cxx
-  DEPENDENCIES
-    Core
-    Thread
   BUILTINS
     TBB
 )
 
+target_link_libraries(Imt PRIVATE Thread INTERFACE Core)
+
 if(imt)
   target_include_directories(Imt PRIVATE ${TBB_INCLUDE_DIRS})
-  target_link_libraries(Imt PUBLIC ${TBB_LIBRARIES})
+  target_link_libraries(Imt PRIVATE ${TBB_LIBRARIES})
 
   ROOT_GENERATE_DICTIONARY(G__Imt STAGE1
     ROOT/TFuture.hxx