Allow 'small-build' and 'big-build' to be used as options.

These two flags are already tested in tools/toolchains/gcc.py but can't
be used at the moment because they are not part of the argument list of
the option parameter.

tools/options.py

@@ -75,7 +75,9 @@ def get_default_options_parser(add_clean=True, add_options=True):
                                   'run Goanna static code analyzer")'),
                             type=argparse_lowercase_hyphen_type(['save-asm',
                                                                  'debug-info',
-                                                                 'analyze'],
+                                                                 'analyze',
+								 'small-build',
+								 'big-build'],
                                                                 "build option"))
 
     return parser