avoid invalidations when it doesn't resolve an MethodError

In these cases, the new method would not be called because the
call would still be an ambiguity error instead.

We also might observe that the method doesn't resolve an old MethodError
because it was previously covered by a different method.

Author: vtjnash

src/gc.c

@@ -2641,6 +2641,7 @@ mark: {
 
 extern jl_typemap_entry_t *call_cache[N_CALL_CACHE];
 extern jl_array_t *jl_all_methods;
+extern jl_array_t *_jl_debug_method_invalidation;
 
 static void jl_gc_queue_thread_local(jl_gc_mark_cache_t *gc_cache, jl_gc_mark_sp_t *sp,
                                      jl_ptls_t ptls2)
@@ -2680,6 +2681,8 @@ static void mark_roots(jl_gc_mark_cache_t *gc_cache, jl_gc_mark_sp_t *sp)
             gc_mark_queue_obj(gc_cache, sp, call_cache[i]);
     if (jl_all_methods != NULL)
         gc_mark_queue_obj(gc_cache, sp, jl_all_methods);
+    if (_jl_debug_method_invalidation != NULL)
+        gc_mark_queue_obj(gc_cache, sp, _jl_debug_method_invalidation);
 
     // constants
     gc_mark_queue_obj(gc_cache, sp, jl_emptytuple_type);