dwarf2out: Fix -gsplit-dwarf on riscv [PR103874]

dwarf2out: Fix -gsplit-dwarf on riscv [PR103874]

riscv*-*-* are the only modern targets that !HAVE_AS_LEB128 (apparently
due to some aggressive linker optimizations).
As the following testcase shows, we mishandle in index_rnglists the
!HAVE_AS_LEB128 && !have_multiple_function_sections case.

output_rnglists does roughly:
  FOR_EACH_VEC_SAFE_ELT (ranges_table, i, r)
    {
...
      if (block_num > 0)
        {
...
          if (HAVE_AS_LEB128)
            {
              if (!have_multiple_function_sections)
                {
                  // code not using r->*_entry
                  continue;
                }
              // code that sometimes doesn't use r->*_entry,
              // sometimes r->begin_entry
            }
          else if (dwarf_split_debug_info)
            {
              // code that uses both r->begin_entry and r->end_entry
            }
          else
            {
              // code not using r->*_entry
            }
        }
      else if (block_num < 0)
        {
          if (!have_multiple_function_sections)
            gcc_unreachable ();
...
        }
    }
and index_rnglists is what sets up those r->{begin,end}_entry members.
The code did an early if (!have_multiple_function_sections) continue;
which is fine for the HAVE_AS_LEB128 case, because r->*_entry is not
used in that case, but not for !HAVE_AS_LEB128 that uses it anyway.

2022-01-20  Jakub Jelinek  <jakub@redhat.com>

	PR debug/103874
	* dwarf2out.cc (index_rnglists): For !HAVE_AS_LEB128 and
	block_num > 0, index entry even if !have_multiple_function_sections.

	* gcc.dg/debug/dwarf2/pr103874.c: New test.