This allows customising which features can be enabled in a frozen library.
e.g. `include("path.py", extra_features=True)`
in path.py:
options.defaults(standard_features=True)
if options.standard_features:
# freeze standard modules.
if options.extra_features:
# freeze extra modules.
Signed-off-by: Jim Mussared <jim.mussared@gmail.com>
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