[clang] [clang][dataflow] Allow `DataflowAnalysisContext` to use a non-owned `Solver`. (PR #91316)

[Mehdi Amini via cfe-commits]

joker-eph wrote:

Actually your premerge failure here was an infra issue, but the CI is still broken after this PR somehow: https://lab.llvm.org/buildbot/#/builders/271/builds/7420

https://github.com/llvm/llvm-project/pull/91316