Squash readelf warning on zero sh_link reloc section

Squash readelf warning on zero sh_link reloc section

On readelf examining a static executable built with current glibc,
we get a silly warning.

Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            0000000000000000 000000 000000 00      0   0  0
  [ 1] .note.ABI-tag     NOTE            0000000000400190 000190 000020 00   A  0   0  4
  [ 2] .note.gnu.build-id NOTE            00000000004001b0 0001b0 000024 00   A  0   0  4
readelf: Warning: [ 3]: Link field (0) should index a symtab section.
  [ 3] .rela.plt         RELA            00000000004001d8 0001d8 000228 18  AI  0  20  8

This .rela.plt section contains only IRELATIVE relocations (which have
symbol index zero), so it isn't appropriate to warn.  A zero sh_link
section is deliberately chosen for such a section (see PR10337 and
PR23850).

So this patch disables the SHT_REL* sh_link warning.  I've also
removed the .rel.dyn/.rela.dyn section name test to disable the
sh_info warning for SHT_REL* sections.  While relocation sections in
an executable need not specify the section they relocate (the
relocation sh_offset field is an address, not a section offset), that
isn't true in a relocatable file where sh_offset is relative to a
section.  If .rela.dyn happens to exist in an ET_REL object it must
specify a valid section.

	* readelf.c (process_section_headers): Don't warn on a zero
	sh_info or sh_link for any reloc section in an executable or
	shared library.  Do warn for .rel.dyn/.rela.dyn in ET_REL.