Add regex dependency to librustc_mir

Cargo.lock

@@ -3758,6 +3758,7 @@ dependencies = [
  "itertools 0.8.2",
  "log_settings",
  "polonius-engine",
+ "regex",
  "rustc_apfloat",
  "rustc_ast",
  "rustc_attr",

compiler/rustc_mir/Cargo.toml

@@ -14,6 +14,7 @@ itertools = "0.8"
 tracing = "0.1"
 log_settings = "0.1.1"
 polonius-engine = "0.12.0"
+regex = "1"
 rustc_middle = { path = "../rustc_middle" }
 rustc_attr = { path = "../rustc_attr" }
 rustc_data_structures = { path = "../rustc_data_structures" }