ZJIT: Fix crash when Kernel is prepended before JIT init

Use RCLASS_ORIGIN when looking up methods to register for specialized
codegen. Module#prepend moves original methods to an origin iclass,
so rb_method_entry_at on the module itself returns NULL after prepend.

This happens in practice when BUNDLER_SETUP triggers Kernel.prepend
during ruby_init_prelude, before rb_zjit_init runs.

Author: rwstauner

zjit/src/cruby_methods.rs

@@ -78,7 +78,8 @@ fn annotate_c_method(props_map: &mut HashMap<*mut c_void, FnProperties>, class:
         // TODO(alan): (side quest) make rust methods and clean up glue code for rb_method_cfunc_t and
         // rb_method_definition_t.
         let method_id = rb_intern2(method_name.as_ptr().cast(), method_name.len() as _);
-        let method = rb_method_entry_at(class, method_id);
+        // Use RCLASS_ORIGIN to find methods that were moved by Module#prepend
+        let method = rb_method_entry_at(RCLASS_ORIGIN(class), method_id);
         assert!(!method.is_null());
         // ME-to-CME cast is fine due to identical layout
         debug_assert_eq!(VM_METHOD_TYPE_CFUNC, get_cme_def_type(method.cast()));
@@ -93,7 +94,8 @@ fn annotate_c_method(props_map: &mut HashMap<*mut c_void, FnProperties>, class:
 fn annotate_builtin_method(props_map: &mut HashMap<*mut c_void, FnProperties>, class: VALUE, method_name: &'static str, props: FnProperties) {
     unsafe {
         let method_id = rb_intern2(method_name.as_ptr().cast(), method_name.len().try_into().unwrap());
-        let method = rb_method_entry_at(class, method_id);
+        // Use RCLASS_ORIGIN to find methods that were moved by Module#prepend
+        let method = rb_method_entry_at(RCLASS_ORIGIN(class), method_id);
         if method.is_null() {
             panic!("Method {}#{} not found", std::ffi::CStr::from_ptr(rb_class2name(class)).to_str().unwrap_or("?"), method_name);
         }