root-toolfile: change ROOT_INCLUDE_PATH to Clang-like

Cling/rootcling is like a wrapper for Driver in some sense. It needs
to be treated as Clang compiler, thus default path must be as Clang
sees them, not GCC.

Additional add ROOT include path as the first.

Signed-off-by: David Abdurachmanov <David.Abdurachmanov@cern.ch>