Add a PT_NOTE section to mark build_id.

nacl/dyn-link/ldscripts/elf64_nacl.xs

 /* Script for ld --shared: link shared library */
 OUTPUT_FORMAT("elf64-nacl", "elf64-nacl",
               "elf64-nacl")
 OUTPUT_ARCH(i386:x86-64)
 ENTRY(_start)
 SEARCH_DIR("=/usr/local/lib"); SEARCH_DIR("=/lib"); SEARCH_DIR("=/usr/lib");
 PHDRS
 {
   seg_code     PT_LOAD FLAGS(5) ;       /* read + execute */
   seg_rodata   PT_LOAD FLAGS(4) ;       /* read */
   seg_rwdata   PT_LOAD FLAGS(6) ;       /* read + write */
   seg_bss      PT_LOAD FLAGS(6) ;       /* read + write */
   seg_dynamic  PT_DYNAMIC FLAGS(6) ;
   seg_stack    PT_GNU_STACK FLAGS(6) ;
   seg_tls      PT_TLS FLAGS(4) ;
+  seg_note     PT_NOTE FLAGS(4) ;
 }
 SECTIONS
 {
   . = SEGMENT_START("text", 0);
   _begin = .;
 
   /* The ALIGN(32) instructions below are workarounds.
      TODO(mseaborn): Get the object files to include the correct
      alignments and padding themselves.
      See http://code.google.com/p/nativeclient/issues/detail?id=499. */
@@ skipping 19 matching lines @@
   PROVIDE (__etext = .);
   PROVIDE (_etext = .);
   PROVIDE (etext = .);
 
   . = ALIGN(SEGMENT_START("text", 0) + 0x10000000, CONSTANT (MAXPAGESIZE));
   .note.gnu.build-id :
   {
     PROVIDE_HIDDEN (__note_gnu_build_id_start = .);
     *(.note.gnu.build-id)
     PROVIDE_HIDDEN (__note_gnu_build_id_end = .);
-  } :seg_rodata
+  } :seg_rodata :seg_note
+  .dummy : {} : seg_rodata
   .hash           : { *(.hash) }
   .gnu.hash       : { *(.gnu.hash) }
   .dynsym         : { *(.dynsym) }
   .dynstr         : { *(.dynstr) }
   .gnu.version    : { *(.gnu.version) }
   .gnu.version_d  : { *(.gnu.version_d) }
   .gnu.version_r  : { *(.gnu.version_r) }
   .rel.init       : { *(.rel.init) }
   .rela.init      : { *(.rela.init) }
   .rel.text       : { *(.rel.text .rel.text.* .rel.gnu.linkonce.t.*) }
@@ skipping 163 matching lines @@
   .debug_funcnames 0 : { *(.debug_funcnames) }
   .debug_typenames 0 : { *(.debug_typenames) }
   .debug_varnames  0 : { *(.debug_varnames) }
   /* DWARF 3 */
   .debug_pubtypes 0 : { *(.debug_pubtypes) }
   .debug_ranges   0 : { *(.debug_ranges) }
   .gnu.attributes 0 : { KEEP (*(.gnu.attributes)) }
   /DISCARD/ : { *(.note.GNU-stack) *(.gnu_debuglink) }
   /DISCARD/ : { *(.note.ABI-tag) }
 }