math/z3: Update 4.15.4.0 => 4.15.8.0

[alven]

Summary

Changelogs:

• https://github.com/Z3Prover/z3/blob/master/RELEASE_NOTES.md#version-4158
• https://github.com/Z3Prover/z3/compare/z3-4.15.4...z3-4.15.5
• https://github.com/Z3Prover/z3/compare/z3-4.15.5...z3-4.15.6
• https://github.com/Z3Prover/z3/compare/z3-4.15.6...z3-4.15.7
• https://github.com/Z3Prover/z3/compare/z3-4.15.7...z3-4.15.8

Test Plan

For every {150amd64, 143amd64, 143i386}:

• Successful poudriere testport
• Successful run-testing