runtime: use naked function for IRQ

non-naked IRQ would somehow trigger interrupts after several kernel
restarts, investigating

src/runtime/src/irq.rs

@@ -16,6 +16,7 @@ static CORE1_RESTART: AtomicBool = AtomicBool::new(false);
 
 #[link_section = ".text.boot"]
 #[no_mangle]
+#[naked]
 pub unsafe extern "C" fn IRQ() {
     if MPIDR.read().cpu_id() == 1 {
         let mpcore = mpcore::RegisterBlock::mpcore();

src/runtime/src/main.rs

@@ -6,6 +6,7 @@
 #![feature(c_variadic)]
 #![feature(const_btree_new)]
 #![feature(const_in_array_repeat_expressions)]
+#![feature(naked_functions)]
 
 extern crate alloc;