[clang] [CIR] Initial implementation of lowering CIR to MLIR (PR #127835)

[Andy Kaylor via cfe-commits]

================
@@ -2958,6 +2958,8 @@ defm clangir : BoolFOption<"clangir",
   BothFlags<[], [ClangOption, CC1Option], "">>;
 def emit_cir : Flag<["-"], "emit-cir">, Visibility<[ClangOption, CC1Option]>,
   Group<Action_Group>, HelpText<"Build ASTs and then lower to ClangIR">;
+def emit_cir_mlir : Flag<["-"], "emit-cir-mlir">, Visibility<[CC1Option]>, Group<Action_Group>,
----------------
andykaylor wrote:

> If we add `emit_mlir_EQ` will that peacefully coexist with the `def emit_mlir : Flag<["-"], "emit-mlir">, Alias<emit_fir>;` definition until we can update flang to align the behavior of the option with no argument?

Answering my own question, yes, it will peacefully coexist. At least, the clang part of it worked. I can't see a reason that flang would be impacted (functionally) by what I did here, but I didn't build and test flang.

I think it makes sense to put `emit_mlir_EQ` in here and then have a separate PR to have flang make use of this option, adding the additional flang dialects, and flang-specific help text.

https://github.com/llvm/llvm-project/pull/127835