Fix: Have _resolve_scheme check prefix availability

[cielavenir]

            if self.prefix is None:
                if self.exec_prefix is not None:
                    raise DistutilsOptionError(
                        "must not supply exec-prefix without prefix"
                    )

                # Allow Fedora to add components to the prefix
                _prefix_addition = getattr(sysconfig, '_prefix_addition', "")

                self.prefix = os.path.normpath(sys.prefix) + _prefix_addition
                self.exec_prefix = os.path.normpath(sys.exec_prefix) + _prefix_addition

            else:
                if self.exec_prefix is None:
                    self.exec_prefix = self.prefix

            self.install_base = self.prefix
            self.install_platbase = self.exec_prefix
            self.select_scheme("posix_prefix")

Here _prefix_addition is considered only when self.prefix is only None.

Meanwhile, select_scheme("posix_prefix") becomes select_scheme("posix_local") on Debian 12+ unconditionally.

self.prefix should be considered.

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This is basically for setup.py install --prefix=. For pip install --prefix=, see pypa/pip#13634 .