Update pnacl toolchain version

ports/pnacl/compiler_wrapper.py

 #!/usr/bin/env python
 # Copyright (c) 2016 The Native Client Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Compiler wrapper for injecting extra libs at the end of the link
 line.
 
 This is used rather than just setting LDFLAGS/LIBS becuase setting
 LIBS/LDFLAGS will effect both host and target builds.
 """
 
 import os
 import subprocess
 import sys
 
 cmd = sys.argv[1:]
 
-# Add extra libs when linking
+is_configuring = 'conftest.c' in cmd or 'conftest.pexe' in cmd
 is_linking = '-c' not in cmd and '-E' not in cmd
-if is_linking:
-  cmd += os.environ['EXTRA_LIBS'].split()
+is_shared = '-shared' in cmd
+
+# Add extra libs when linking executables
+if is_linking and not is_shared:
+  cmd += os.environ['WEBPORTS_EXTRA_LIBS'].split()
+
+if is_configuring:
+  cmd.remove('-include')
+  cmd.remove('spawn.h')
 
 sys.exit(subprocess.call(cmd))