[mlir] [llvm] [mlir] Add config for PDL (PR #69927)

[Mehdi Amini via llvm-commits]

https://github.com/joker-eph commented:

Look pretty good to me overall! 

> MLIR is a general infrastructure and as far as possible no dialect is intended to be special or privileged (we have Builtin which is both and should be addressed ...). Users should be able to use MLIR and the parts they need to customize for their solution (e.g., one doesn't have to include any dialect except the ones one uses). 

Can you rework the description please? I feel it is misleading.
PDL/PDLL are dialects for the pattern rewrite infra, and what you're doing is making is possible for the "pattern rewrite infrastructure" to statically disable support for PD/PDLL. This does not make any dialect more "privileged", or "special". The fact that these are "dialects" is anecdotical: we could have written a different DSL with a custom bytecode interpret without using MLIR dialect just as well. The misleading part is that this is describing this in the say way as if these were dialects like the others, intended to blend in the compiler ecosystem.

https://github.com/llvm/llvm-project/pull/69927