Revision 1900882

Replace a call to a function deprecated upstream.

The behaviour of «ConfigParser.readfp(foo)» has changed across Python versions
as follows:

- Python 3.1: readfp(foo) would repeatedly call foo.readline().

- Python 3.2 through 3.11: readfp(foo) iterates foo.

- Python 3.12: readfp itself would be removed (according to a deprecation
    warning that 3.10's readfp() emits).

Patch by: Hugo
Issue: SVN-4899 (in part)

* build/generator/gen_base.py
  (GeneratorBase.__init__): As above.