Fix the linker's handling of DWARF-5 line number tables.

Fix the linker's handling of DWARF-5 line number tables.

When building with gcc with -gdwarf-5 ld tests (including ld-elf/dwarf.exp)
fail because they try to read the .debug_ranges section. But DWARF5
introduces a new .debug_rnglists section that encodes the address ranges
more efficiently. Implement reading the debug_rnglists in bfd/dwarf2.c.
Which makes all tests pass again and fixes several gcc testsuite tests
when defaulting to DWARF5.

	*  dwarf2.c (struct dwarf2_debug_file): Add dwarf_rnglists_buffer
	and dwarf_rnglists_size fields.
	(dwarf_debug_sections): Add debug_rnglists.
	(dwarf_debug_section_enum): Likewise.
	(read_debug_rnglists): New function.
	(read_rangelist): New function to call either read_ranges or
	read_rnglists. Rename original function to...
	(read_ranges): ...this.
	(read_rnglists): New function.