[clang] [CIR] Add cir-simplify pass (PR #138317)

[Erich Keane via cfe-commits]

================
@@ -27,6 +27,8 @@ def CIR_Dialect : Dialect {
   let useDefaultAttributePrinterParser = 0;
   let useDefaultTypePrinterParser = 0;
 
+  let hasConstantMaterializer = 1;
----------------
erichkeane wrote:

oh boy would i love a comment explaining this.

https://github.com/llvm/llvm-project/pull/138317