Add is_intrinsic helper

Author: oli-obk

clippy_utils/src/qualify_min_const_fn.rs

@@ -334,7 +334,7 @@ fn check_terminator<'tcx>(
                 // within const fns. `transmute` is allowed in all other const contexts.
                 // This won't really scale to more intrinsics or functions. Let's allow const
                 // transmutes in const fn before we add more hacks to this.
-                if matches!(tcx.intrinsic(fn_def_id), Some(sym::transmute)) {
+                if tcx.is_intrinsic(fn_def_id, sym::transmute) {
                     return Err((
                         span,
                         "can only call `transmute` from const items, not `const fn`".into(),