Remove skeleton type units that were being produced with -gsplit-dwarf.

Remove skeleton type units that were being produced with -gsplit-dwarf.

These sections were originally intended as targets for .gdb_index
entries that needed to point to type units.  Because of the limitations
of the .debug_gnu_pubnames/pubtypes sections with split DWARF, we were
not able to pass along enough information to the gold linker to generate
those index entries properly, and they had to point to the CU instead.
GDB had to deal with that, and was updated a while ago to no longer
depend on the skeleton TU sections at all. This allows us to reduce
object file sizes with split DWARF by about 30%.

gcc/
	* dwarf2out.c (get_skeleton_type_unit): Remove.
	(output_skeleton_debug_sections): Remove skeleton type units.
	(output_comdat_type_unit): Likewise.
	(dwarf2out_finish): Likewise.

From-SVN: r213765