objcopy --only-keep-debug

From: Peilin Ye <peilin.ye@bytedance.com>
objcopy's --only-keep-debug option has been broken for ELF files since
commit 8c803a2dd7.

  1. binutils/objcopy.c:setup_section() marks non-debug sections as
     SHT_NOBITS, then calls bfd_copy_private_section_data();
  2. If ISEC and OSEC share the same section flags,
     bfd/elf.c:_bfd_elf_init_private_section_data() restores OSEC's
     section type back to ISEC's section type, effectively undoing
     "make_nobits".

	* objcopy.c (setup_section): Act on make_nobits after calling
	bfd_copy_private_section_data.

binutils/objcopy.c

@@ -4085,9 +4085,6 @@ setup_section (bfd *ibfd, sec_ptr isection, void *obfdarg)
       goto loser;
     }
 
-  if (make_nobits)
-    elf_section_type (osection) = SHT_NOBITS;
-
   size = bfd_section_size (isection);
   size = bfd_convert_section_size (ibfd, isection, obfd, size);
   if (copy_byte >= 0)
@@ -4181,6 +4178,9 @@ setup_section (bfd *ibfd, sec_ptr isection, void *obfdarg)
       goto loser;
     }
 
+  if (make_nobits)
+    elf_section_type (osection) = SHT_NOBITS;
+
   /* All went well.  */
   return;