Add a PT_NOTE section to mark build_id.

elf/nacl_fixup_ldso.py

Index: elf/nacl_fixup_ldso.py
diff --git a/elf/nacl_fixup_ldso.py b/elf/nacl_fixup_ldso.py
index f60becc06562b538cd5ede5adc7be0e4def1852e..a5eb1f9eea1e32680b10909f76a2c97bb4ab61b1 100644
--- a/elf/nacl_fixup_ldso.py
+++ b/elf/nacl_fixup_ldso.py
@@ -48,10 +48,10 @@ def main(args):
     fh.seek(offset_ei_class)
     elfclass = fh.read(1)
     if elfclass == elfclass32:
-        check("H", offset_e_phnum32, 6)
+        check("H", offset_e_phnum32, 7)
         replace("H", offset_e_phnum32, 3)
     elif elfclass == elfclass64:
-        check("H", offset_e_phnum64, 6)
+        check("H", offset_e_phnum64, 7)
         replace("H", offset_e_phnum64, 3)
     else:
         raise AssertionError("Unknown ELF class in file %s." % filename)