Use std_or_core to determine the correct prefix

Replace hand-crafted tests by the a call to the `std_or_core()` utility
function.

clippy_lints/src/casts/borrow_as_ptr.rs

@@ -1,6 +1,6 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::is_no_std_crate;
 use clippy_utils::source::snippet_with_context;
+use clippy_utils::std_or_core;
 use rustc_errors::Applicability;
 use rustc_hir::{BorrowKind, Expr, ExprKind, Mutability, Ty, TyKind};
 use rustc_lint::LateContext;
@@ -16,8 +16,8 @@ pub(super) fn check<'tcx>(
 ) {
     if matches!(cast_to.kind, TyKind::Ptr(_))
         && let ExprKind::AddrOf(BorrowKind::Ref, mutability, e) = cast_expr.kind
+        && let Some(std_or_core) = std_or_core(cx)
     {
-        let core_or_std = if is_no_std_crate(cx) { "core" } else { "std" };
         let macro_name = match mutability {
             Mutability::Not => "addr_of",
             Mutability::Mut => "addr_of_mut",
@@ -40,7 +40,7 @@ pub(super) fn check<'tcx>(
             expr.span,
             "borrow as raw pointer",
             "try",
-            format!("{core_or_std}::ptr::{macro_name}!({snip})"),
+            format!("{std_or_core}::ptr::{macro_name}!({snip})"),
             Applicability::MachineApplicable,
         );
     }

clippy_lints/src/casts/ref_as_ptr.rs

@@ -1,7 +1,7 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::source::snippet_with_applicability;
 use clippy_utils::sugg::Sugg;
-use clippy_utils::{ExprUseNode, expr_use_ctxt, is_no_std_crate};
+use clippy_utils::{ExprUseNode, expr_use_ctxt, std_or_core};
 use rustc_errors::Applicability;
 use rustc_hir::{Expr, Mutability, Ty, TyKind};
 use rustc_lint::LateContext;
@@ -25,8 +25,8 @@ pub(super) fn check<'tcx>(
         && let use_cx = expr_use_ctxt(cx, expr)
         // TODO: only block the lint if `cast_expr` is a temporary
         && !matches!(use_cx.use_node(cx), ExprUseNode::LetStmt(_) | ExprUseNode::ConstStatic(_))
+        && let Some(std_or_core) = std_or_core(cx)
     {
-        let core_or_std = if is_no_std_crate(cx) { "core" } else { "std" };
         let fn_name = match to_mutbl {
             Mutability::Not => "from_ref",
             Mutability::Mut => "from_mut",
@@ -56,7 +56,7 @@ pub(super) fn check<'tcx>(
             expr.span,
             "reference as raw pointer",
             "try",
-            format!("{core_or_std}::ptr::{fn_name}{turbofish}({cast_expr_sugg})"),
+            format!("{std_or_core}::ptr::{fn_name}{turbofish}({cast_expr_sugg})"),
             app,
         );
     }

clippy_lints/src/loops/missing_spin_loop.rs

@@ -1,6 +1,6 @@
 use super::MISSING_SPIN_LOOP;
 use clippy_utils::diagnostics::span_lint_and_sugg;
-use clippy_utils::is_no_std_crate;
+use clippy_utils::std_or_core;
 use rustc_errors::Applicability;
 use rustc_hir::{Block, Expr, ExprKind};
 use rustc_lint::LateContext;
@@ -41,19 +41,15 @@ pub(super) fn check<'tcx>(cx: &LateContext<'tcx>, cond: &'tcx Expr<'_>, body: &'
         && [sym::load, sym::compare_exchange, sym::compare_exchange_weak].contains(&method.ident.name)
         && let ty::Adt(def, _args) = cx.typeck_results().expr_ty(callee).kind()
         && cx.tcx.is_diagnostic_item(sym::AtomicBool, def.did())
+        && let Some(std_or_core) = std_or_core(cx)
     {
         span_lint_and_sugg(
             cx,
             MISSING_SPIN_LOOP,
             body.span,
             "busy-waiting loop should at least have a spin loop hint",
             "try",
-            (if is_no_std_crate(cx) {
-                "{ core::hint::spin_loop() }"
-            } else {
-                "{ std::hint::spin_loop() }"
-            })
-            .into(),
+            format!("{{ {std_or_core}::hint::spin_loop() }}"),
             Applicability::MachineApplicable,
         );
     }