Tidy some include usage + dependencies

Tidy some include usage + dependencies

The dwarf2out.c and lto-streamer-in.c files didn't need
libfuncs.h in the first place.  The libfuncs.h file will
grow a use of an optab enumeration and thus will require
including optabs.h.

        * libfuncs.h: Include optabs.h.
        * dwarf2out.c, lto-streamer.in.c: Don't include libfuncs.h.
        * Makefile.in (LIBFUNCS_H): Add OPTABS_H.
        (lto-streamer-in.o, dwarf2out.o): Update deps.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@189817 138bc75d-0d04-0410-961f-82ee72b054a4