SConstruct: make help work even if guesses failed.

SConstruct

 # Copyright 2010 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 647 matching lines @@
 
 OS_GUESS = utils.GuessOS()
 TOOLCHAIN_GUESS = GuessToolchain(OS_GUESS)
 ARCH_GUESS = utils.GuessArchitecture()
 
 
 SIMPLE_OPTIONS = {
   'toolchain': {
     'values': ['gcc', 'msvc'],
     'default': TOOLCHAIN_GUESS,
-    'help': 'the toolchain to use (' + TOOLCHAIN_GUESS + ')'
+    'help': 'the toolchain to use (%s)' % TOOLCHAIN_GUESS
   },
   'os': {
     'values': ['freebsd', 'linux', 'macos', 'win32', 'android', 'openbsd', 'solaris'],
     'default': OS_GUESS,
-    'help': 'the os to build for (' + OS_GUESS + ')'
+    'help': 'the os to build for (%s)' % OS_GUESS
   },
   'arch': {
     'values':['arm', 'ia32', 'x64', 'mips'],
     'default': ARCH_GUESS,
-    'help': 'the architecture to build for (' + ARCH_GUESS + ')'
+    'help': 'the architecture to build for (%s)' % ARCH_GUESS
   },
   'regexp': {
     'values': ['native', 'interpreted'],
     'default': 'native',
     'help': 'Whether to use native or interpreted regexp implementation'
   },
   'snapshot': {
     'values': ['on', 'off', 'nobuild'],
     'default': 'off',
     'help': 'build using snapshots for faster start-up'
@@ skipping 450 matching lines @@
 # version of scons.  Also, there's a bug in some revisions that
 # doesn't allow this flag to be set, so we swallow any exceptions.
 # Lovely.
 try:
   SetOption('warn', 'no-deprecated')
 except:
   pass
 
 
 Build()