cpp.texi: Update for -MT.

        * cpp.texi: Update for -MT.
        * cppinit.c (initialize_dependency_output): Add a default
        target if none has been given already.
        (no_tgt, OPT_MT): New.
        (cpp_handle_option): Handle -MT.  Update -M etc.
        * cpplib.h (struct cpp_options): Remove deps_target.
        * gcc.c (cpp_options): Handle -MT.
        * mkdeps.c (struct deps): Move from mkdeps.h.
        (deps_calc_target): Rename deps_add_default_target.  Add a
        default target if none has been specified already.
        * mkdeps.h (struct deps): Move to mkdeps.c.
        (deps_calc_target): Rename deps_add_default_target.

From-SVN: r38681