tests: codegen-llvm: Use minicore in bpf-alu32

Instead of keeping it as `only-bpf`, use minicore. This way we make sure
it will never get outdated again.

Author: vadorovsky

tests/codegen-llvm/bpf-alu32.rs

@@ -1,8 +1,14 @@
-//@ only-bpf
+//@ add-minicore
+//@ compile-flags: --target=bpfel-unknown-none
+//@ needs-llvm-components: bpf
 #![crate_type = "lib"]
-#![feature(bpf_target_feature)]
+#![feature(bpf_target_feature, no_core)]
+#![no_core]
 #![no_std]
 
+extern crate minicore;
+use minicore::*;
+
 #[no_mangle]
 #[target_feature(enable = "alu32")]
 // CHECK: define noundef zeroext i8 @foo(i8 noundef returned %arg) unnamed_addr #0 {