[llvm] Bump required minimal Z3 version from 4.7.1 to 4.8.9 (PR #96682)

[via llvm-commits]

whisperity wrote:

Most precisely speaking I'm not a CSA dev, so there is no possibility for this to block me, but maybe @balazske and @NagyDonat should cross-check if they're using Z3 for anything and if they can self-compile the newer versions of Z3 instead of using the system one.

https://github.com/llvm/llvm-project/pull/96682