Use cfg!() rather than #[cfg] for the cfg in map_memory

src/startup/memory.rs

@@ -276,8 +276,7 @@ unsafe fn map_memory<A: Arch>(areas: &[MemoryArea], mut bump_allocator: &mut Bum
     let mut mapper = PageMapper::<A, _>::create(TableKind::Kernel, &mut bump_allocator)
         .expect("failed to create Mapper");
 
-    #[cfg(target_arch = "x86")]
-    {
+    if cfg!(target_arch = "x86") {
         // Pre-allocate all kernel PD entries so that when the page table is copied,
         // these entries are synced between processes
         for i in 512..1024 {