[NaCl SDK] Re-land "Added support for NaCl IO to use the IRT Extension API."

native_client_sdk/src/libraries/nacl_io/library.dsc

 {
   'TOOLS': ['newlib', 'glibc', 'bionic', 'pnacl', 'linux', 'mac', 'clang-newlib'],
   'SEARCH': [
     '.',
     'pepper',
     '../third_party/newlib-extras',
     'include',
   ],
   'TARGETS': [
     {
@@ skipping 22 matching lines @@
         "in6_addr.c",
         "jsfs/js_fs.cc",
         "jsfs/js_fs_node.cc",
         "kernel_handle.cc",
         "kernel_intercept.cc",
         "kernel_object.cc",
         "kernel_proxy.cc",
         "kernel_wrap_bionic.cc",
         "kernel_wrap_dummy.cc",
         "kernel_wrap_glibc.cc",
+        "kernel_wrap_irt_ext.c",
         "kernel_wrap_newlib.cc",
         "kernel_wrap_win.cc",
         "log.c",
         "memfs/mem_fs.cc",
         "memfs/mem_fs_node.cc",
         "nacl_io.cc",
         "node.cc",
         "passthroughfs/passthrough_fs.cc",
         "passthroughfs/real_node.cc",
         "path.cc",
@@ skipping 229 matching lines @@
         "all_interfaces.h",
         "define_empty_macros.h",
         "undef_macros.h",
       ],
       'DEST': 'include/nacl_io/pepper',
     }
   ],
   'DEST': 'src',
   'NAME': 'nacl_io',
 }