[llvm] [mlir] [CMake] Add dependent project mode for Flang's MLIR (PR #221724)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

> Did you build to measure number of files affected / build time / size?

Yes, before the patch 442 libMLIR*.a targets were reachable. Afterward, 317 remain—about 72% (or a 28% reduction).

We have more room to improve, right now  Flang repeatedly links the complete global MLIR_DIALECT_LIBS and   MLIR_EXTENSION_LIBS collections. A follow-up PR will clean this up as well.

https://github.com/llvm/llvm-project/pull/221724