Contracts core intrinsics.

These are hooks to:

  1. control whether contract checks are run
  2. allow 3rd party tools to intercept and reintepret the results of running contracts.

compiler/rustc_span/src/symbol.rs

@@ -566,6 +566,7 @@ symbols! {
         cfg_attr,
         cfg_attr_multi,
         cfg_boolean_literals,
+        cfg_contract_checks,
         cfg_doctest,
         cfg_emscripten_wasm_eh,
         cfg_eval,
@@ -675,6 +676,9 @@ symbols! {
         const_ty_placeholder: "<const_ty>",
         constant,
         constructor,
+        contract_check_ensures,
+        contract_check_requires,
+        contract_checks,
         convert_identity,
         copy,
         copy_closures,