Make use of -lppapi explicit to allow for correct library order.

native_client_sdk/src/examples/tumbler/example.dsc

 {
   'TOOLS': ['newlib'],
   'TARGETS': [
     {
       'NAME' : 'tumbler',
       'TYPE' : 'main',
       'SOURCES' : [
         'callback.h',
         'cube.cc',
         'cube.h',
         'opengl_context.cc',
         'opengl_context.h',
         'opengl_context_ptrs.h',
         'scripting_bridge.cc',
         'scripting_bridge.h',
         'shader_util.cc',
         'shader_util.h',
         'transforms.cc',
         'transforms.h',
         'tumbler.cc',
         'tumbler.h',
         'tumbler_module.cc'
       ],
-      'LIBS': ['ppapi_cpp', 'ppapi_gles2']
+      'LIBS': ['ppapi_gles2', 'ppapi_cpp', 'ppapi', 'pthread']
     }
   ],
   'DATA': [
     'bind.js',
     'dragger.js',
     'trackball.js',
     'tumbler.js',
     'vector3.js'
   ],
   'DEST': 'examples',
   'NAME': 'tumbler',
   'TITLE': 'Tumbler',
   'DESC': """
 The Tumbler example demonstrates how to create a 3D cube that you can
 rotate with your mouse while pressing the left mouse button. This example
 creates a 3D context and draws to it using OpenGL ES. The JavaScript
 implements a virtual trackball interface to map mouse movements into 3D
 rotations using simple 3D vector math and quaternions.""",
   'INFO': '3D graphics'
 }