Add a query for checking whether a function is an intrinsic.

Author: oli-obk

clippy_utils/src/qualify_min_const_fn.rs

@@ -14,7 +14,6 @@ use rustc_middle::ty::{self, adjustment::PointerCast, Ty, TyCtxt};
 use rustc_semver::RustcVersion;
 use rustc_span::symbol::sym;
 use rustc_span::Span;
-use rustc_target::spec::abi::Abi::RustIntrinsic;
 use std::borrow::Cow;
 
 type McfResult = Result<(), (Span, Cow<'static, str>)>;
@@ -323,7 +322,7 @@ fn check_terminator<'a, '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 tcx.fn_sig(fn_def_id).abi() == RustIntrinsic && tcx.item_name(fn_def_id) == sym::transmute {
+                if tcx.is_intrinsic(fn_def_id) && tcx.item_name(fn_def_id) == sym::transmute {
                     return Err((
                         span,
                         "can only call `transmute` from const items, not `const fn`".into(),