RootUtils: cmake fix for clang compilation

Only the RootUtilsPyROOT library should depend on the pyroot libraries (ROOTTPython and cppyy). In particular, the RootUtils library should not depend on these libraries.

Things were failing in the clang build because RootUtils was linking against cppyy but not against python, so things downstream were failing to find python symbols.

(In principle this is wrong for the gcc build as well; not entirely sure why it was working there.)

Control/RootUtils/CMakeLists.txt

@@ -9,6 +9,9 @@ find_package( Python COMPONENTS Development )
 find_package( ROOT COMPONENTS RIO Hist Tree Core MathCore ROOTTPython
    cppyy${Python_VERSION_MAJOR}_${Python_VERSION_MINOR} )
 
+set( ROOT_LIBRARIES_PYROOT ${ROOT_LIBRARIES} )
+find_package( ROOT COMPONENTS RIO Hist Tree Core MathCore )
+
 # Component(s) in the package:
 atlas_generate_reflex_dictionary( dict_cpp RootUtils
    HEADER ${CMAKE_CURRENT_SOURCE_DIR}/RootUtils/RootUtilsDict.h
@@ -28,7 +31,7 @@ atlas_add_library( RootUtilsPyROOT
    PUBLIC_HEADERS RootUtils
    INCLUDE_DIRS ${Python_INCLUDE_DIRS} ${Boost_INCLUDE_DIRS}
    ${ROOT_INCLUDE_DIRS}
-   LINK_LIBRARIES ${Python_LIBRARIES} ${Boost_LIBRARIES} ${ROOT_LIBRARIES}
+   LINK_LIBRARIES ${Python_LIBRARIES} ${Boost_LIBRARIES} ${ROOT_LIBRARIES_PYROOT}
    CxxUtils )
 
 atlas_add_dictionary( RootUtilsPyROOTDict