S/390: Fix (some) PIE+undef weak failures

This fixes these failures on 64 bit which currently occur when running
the Binutils testsuite with a default PIE compiler.

< FAIL: Build rdynamic-1
< FAIL: Build dynamic-1
< FAIL: Build pr22269-1

bfd/ChangeLog:

2017-12-13  Andreas Krebbel  <krebbel@linux.vnet.ibm.com>

	* elf64-s390.c (elf_s390_adjust_dynamic_symbol): Use
	UNDEFWEAK_NO_DYNAMIC_RELOC.
	(allocate_dynrelocs): Likewise.
	(elf_s390_relocate_section): Check resolved_to_zero.
	(elf_s390_finish_dynamic_symbol): Don't generate runtime reloc if
	UNDEFWEAK_NO_DYNAMIC_RELOC.

bfd/elf64-s390.c

@@ -1433,8 +1433,7 @@ elf_s390_adjust_dynamic_symbol (struct bfd_link_info *info,
     {
       if (h->plt.refcount <= 0
 	  || SYMBOL_CALLS_LOCAL (info, h)
-	  || (ELF_ST_VISIBILITY (h->other) != STV_DEFAULT
-	      && h->root.type == bfd_link_hash_undefweak))
+	  || UNDEFWEAK_NO_DYNAMIC_RELOC (info, h))
 	{
 	  /* This case can occur if we saw a PLT32 reloc in an input
 	     file, but the symbol was never referred to by a dynamic
@@ -1669,8 +1668,7 @@ allocate_dynrelocs (struct elf_link_hash_entry *h,
 	htab->elf.srelgot->size += sizeof (Elf64_External_Rela);
       else if (tls_type == GOT_TLS_GD)
 	htab->elf.srelgot->size += 2 * sizeof (Elf64_External_Rela);
-      else if ((ELF_ST_VISIBILITY (h->other) == STV_DEFAULT
-		|| h->root.type != bfd_link_hash_undefweak)
+      else if (!UNDEFWEAK_NO_DYNAMIC_RELOC (info, h)
 	       && (bfd_link_pic (info)
 		   || WILL_CALL_FINISH_DYNAMIC_SYMBOL (dyn, 0, h)))
 	htab->elf.srelgot->size += sizeof (Elf64_External_Rela);
@@ -2313,8 +2311,7 @@ elf_s390_relocate_section (bfd *output_bfd,
 							  h)
 		       || (bfd_link_pic (info)
 			   && SYMBOL_REFERENCES_LOCAL (info, h))
-		       || (ELF_ST_VISIBILITY (h->other)
-			   && h->root.type == bfd_link_hash_undefweak))
+		       || resolved_to_zero)
 		{
 		  /* This is actually a static link, or it is a
 		     -Bsymbolic link and the symbol is defined
@@ -3417,6 +3414,9 @@ elf_s390_finish_dynamic_symbol (bfd *output_bfd,
       else if (bfd_link_pic (info)
 	       && SYMBOL_REFERENCES_LOCAL (info, h))
 	{
+	  if (UNDEFWEAK_NO_DYNAMIC_RELOC (info, h))
+	    return TRUE;
+
 	  /* If this is a static link, or it is a -Bsymbolic link and
 	     the symbol is defined locally or was forced to be local
 	     because of a version file, we just want to emit a