[llvm] [Transforms] Allow non-regex Source in SymbolRewriter in case of using ExplicitRewriteDescriptor (PR #154319)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

This looks reasonable to me, but could you please add test coverage for all three cases being changed?

(Or alternatively, we should do a preliminary refactoring to deduplicate this case -- at least at a cursory look, all three implementations are the same?)

https://github.com/llvm/llvm-project/pull/154319