Add a scons pnacl finalize step for pnacl_generate_pexe tests.

tests/barebones/nacl.scons

Index: tests/barebones/nacl.scons
diff --git a/tests/barebones/nacl.scons b/tests/barebones/nacl.scons
index eede92149149e9add4e88e4643d6ffab100e76e9..d4e8bfa62b0d8e6a006abe689524e4ec14359ee4 100644
--- a/tests/barebones/nacl.scons
+++ b/tests/barebones/nacl.scons
@@ -22,6 +22,12 @@ env.Replace(LIBS=[],
 if env.Bit('build_arm'):
   env.Append(CPPDEFINES='SMALL_REGS_TEST')
 
+# The barebones_reloc test need symbols preserved, since it provides
+# a stub function for something that normally comes from the libraries.

[Mark Seaborn, 2013/03/28 01:31:34]

What stub function does barebones_reloc provide that it needs symbols preserved?
 I don't see anything in barebones_reloc.c that should break.

[jvoung - send to chromium..., 2013/03/28 15:50:29]

barebones_reloc.c stores to a few tls variables.  The -nostdlib clause prevents
gcc / pnacl-translate from linking the native crtbegin, crtend, etc. files, so
it won't have __nacl_read_tp.

[Mark Seaborn, 2013/03/28 16:44:33]

Do you get a link error here?

I'm not sure why stripping should affect this.  barebones_reloc.c defines its
own __nacl_read_tp, but after recent changes that definition should get hidden
and not used by the __nacl_read_tp references that codegen produces.

Having a -nostdlib option in the translator is arguably a bug (see
https://code.google.com/p/nativeclient/issues/detail?id=3069), so maybe you
could add a TODO here?  Or does dropping TRANSLATEFLAGS=['-nostdlib'] fix the
link error?

[jvoung (off chromium), 2013/03/28 17:54:50]

Yes it's a link error, trying to find __nacl_read_tp.
The definition in barebones_reloc.c will get hidden by stripping yes.  However
-nostdlib in translate flags makes this not link in crtbegin, so it won't find
the version from crtbegin after codegen runs?
Well, I guess there is a difference between what these barebones tests are
trying to do, vs trying to match gcc's -nostdlib behavior with PNaCl.  For the
tests, we probably only cared that -nostdlib prevented libc from being linked in
to minimize the code that we need to translate.  For matching gcc, it also means
not linking in crtbegin, libgcc, libgcc_eh, etc.  That part probably doesn't
matter as much for debugging LLVM.
No it doesn't fix the link error because of 3069.  If I take out
TRANSLATEFLAGS=['-nostdlib'], then libgcc_eh gets linked in, and I end up with 
problems finding malloc.  I think libgcc_eh gets pulled in because crtbegin
depends on __register_frame_info.  

+if env.Bit('bitcode'):
+  env.SetBits('nonstable_bitcode')
+if env.Bit('skip_nonstable_bitcode'):
+  Return()
 
 # NOTE: the x86 linker wants _start() to be the very first function
 FAKE_STARTUP = env.ComponentObject('fake_startup', 'fake_startup.c')