Change __rust_no_alloc_shim_is_unstable to be a function

compiler/rustc_codegen_cranelift/src/allocator.rs

@@ -1,6 +1,7 @@
 //! Allocator shim
 // Adapted from rustc
 
+use cranelift_frontend::{FunctionBuilder, FunctionBuilderContext};
 use rustc_ast::expand::allocator::{
     ALLOCATOR_METHODS, AllocatorKind, AllocatorTy, NO_ALLOC_SHIM_IS_UNSTABLE,
     alloc_error_handler_name, default_fn_name, global_fn_name,
@@ -97,16 +98,31 @@ fn codegen_inner(
     data.define(Box::new([val]));
     module.define_data(data_id, &data).unwrap();
 
-    let data_id = module
-        .declare_data(
-            &mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
-            Linkage::Export,
-            false,
-            false,
-        )
-        .unwrap();
-    let mut data = DataDescription::new();
-    data.set_align(1);
-    data.define(Box::new([0]));
-    module.define_data(data_id, &data).unwrap();
+    {
+        let sig = Signature {
+            call_conv: module.target_config().default_call_conv,
+            params: vec![],
+            returns: vec![],
+        };
+        let func_id = module
+            .declare_function(
+                &mangle_internal_symbol(tcx, NO_ALLOC_SHIM_IS_UNSTABLE),
+                Linkage::Export,
+                &sig,
+            )
+            .unwrap();
+
+        let mut ctx = Context::new();
+        ctx.func.signature = sig;
+        let mut func_ctx = FunctionBuilderContext::new();
+        let mut bcx = FunctionBuilder::new(&mut ctx.func, &mut func_ctx);
+
+        let block = bcx.create_block();
+        bcx.switch_to_block(block);
+        bcx.ins().return_(&[]);
+        bcx.seal_all_blocks();
+        bcx.finalize();
+
+        module.define_function(func_id, &mut ctx).unwrap();
+    }
 }