Start test case for rjmp regression test

This commit introduces a minimal `![no_core]`-test case running on AVR,
that contains the MCWE mentioned in [129301]. The test case itself does
not have any assertions yet, but it shows the minimal set an language
items necessary within the test case.
[129301]: #129301 (comment)

Author: jfrimmel

tests/assembly/avr-rjmp-offsets.rs

@@ -0,0 +1,62 @@
+//@ compile-flags: -Copt-level=s --target=avr-unknown-gnu-atmega328 -C panic=abort
+//@ needs-llvm-components: avr
+//@ assembly-output: emit-asm
+
+#![feature(
+ no_core,
+ lang_items,
+ intrinsics,
+ rustc_attrs,
+ arbitrary_self_types,
+ asm_experimental_arch
+)]
+#![crate_type = "rlib"]
+#![no_core]
+
+#[rustc_builtin_macro]
+macro_rules! asm {
+() => {};
+}
+
+use minicore::ptr;
+
+// CHECK-LABEL: pin_toggling
+#[no_mangle]
+pubfnpin_toggling(){
+let port_b = 0x25as*mutu8;// the I/O-address of PORTB
+loop{
+unsafe{ ptr::write_volatile(port_b,1)};
+delay(500_0000);
+unsafe{ ptr::write_volatile(port_b,2)};
+delay(500_0000);
+}
+}
+
+#[inline(never)]
+fndelay(_:u32){
+unsafe{asm!("nop")};
+}
+
+// FIXME: replace with proper minicore once available (#130693)
+mod minicore {
+#[lang = "sized"]
+pubtraitSized{}
+
+#[lang = "copy"]
+pubtraitCopy{}
+implCopyforu32{}
+implCopyfor&u32{}
+impl<T: ?Sized>Copyfor*mutT{}
+
+pubmod ptr {
+#[inline]
+#[rustc_diagnostic_item = "ptr_write_volatile"]
+pubunsafefnwrite_volatile<T>(dst:*mutT,src:T){
+extern"rust-intrinsic"{
+#[rustc_nounwind]
+pubfnvolatile_store<T>(dst:*mutT,val:T);
+}
+unsafe{volatile_store(dst, src)};
+}
+}
+}