Don't link the artifact to not depend on avr-gcc

This fixes the [build error] caused by the `avr-gcc` (used as linker)
not being available in the Rust CI.

[build error]: #131755 (comment)

Author: jfrimmel

tests/run-make/avr-rjmp-offset/avr-rjmp-offsets.rs

@@ -5,6 +5,7 @@
 #![feature(no_core, lang_items, intrinsics, rustc_attrs)]
 #![no_core]
 #![no_main]
+#![crate_type = "rlib"]
 
 use minicore::ptr;