add patches to bootstrap z3 with python 2.6

[cosmicexplorer]

Problem

We are currently investigating whether z3 can be used instead of clingo for the new concretizer (from #19501). That work is on https://github.com/spack/spack/tree/z3-concretizer -- it doesn't work yet. If we do use z3, some changes will be necessary to support building with python 2.6.

This diff is on top of #20218, see https://github.com/spack/spack/compare/py26-bootstrap...z3-bootstrap-2.6?expand=1 for the diff on top of that change.

Solution

• Add several patches to remove '{}'.format(...) calls, which must be converted to '{0}'.format(...) for python 2.6.

Result

• z3 should be bootstrappable in an environment with only python 2.6 and a C++ compiler. However, this PR should be closed if we find that it is infeasible to use z3 for the new concretizer.

TODO

• Demonstrate a working z3 implementation of the ASP concretizer from Experimental ASP-based concretizer #19501.

[cosmicexplorer]

This no longer appears to be necessary after dropping python 2.6 support!