Add missing writebarrier to rb_func_proc_dup

Because TypedData_Make_Struct both allocates an object and after
xmallocs memory, all added references must always be writebarrier
protected.

Author: jhawthorn

proc.c

@@ -716,12 +716,15 @@ rb_func_proc_dup(VALUE src_obj)
     VALUE proc_obj = TypedData_Make_Struct(rb_obj_class(src_obj), cfunc_proc_t, &proc_data_type, proc);
 
     memcpy(&proc->basic, src_proc, sizeof(rb_proc_t));
+    RB_OBJ_WRITTEN(proc_obj, Qundef, proc->basic.block.as.captured.self);
+    RB_OBJ_WRITTEN(proc_obj, Qundef, proc->basic.block.as.captured.code.val);
 
+    const VALUE *src_ep = src_proc->block.as.captured.ep;
     VALUE *ep = *(VALUE **)&proc->basic.block.as.captured.ep = proc->env + VM_ENV_DATA_SIZE - 1;
-    ep[VM_ENV_DATA_INDEX_FLAGS]   = src_proc->block.as.captured.ep[VM_ENV_DATA_INDEX_FLAGS];
-    ep[VM_ENV_DATA_INDEX_ME_CREF] = src_proc->block.as.captured.ep[VM_ENV_DATA_INDEX_ME_CREF];
-    ep[VM_ENV_DATA_INDEX_SPECVAL] = src_proc->block.as.captured.ep[VM_ENV_DATA_INDEX_SPECVAL];
-    ep[VM_ENV_DATA_INDEX_ENV]     = src_proc->block.as.captured.ep[VM_ENV_DATA_INDEX_ENV];
+    ep[VM_ENV_DATA_INDEX_FLAGS]   = src_ep[VM_ENV_DATA_INDEX_FLAGS];
+    ep[VM_ENV_DATA_INDEX_ME_CREF] = src_ep[VM_ENV_DATA_INDEX_ME_CREF];
+    ep[VM_ENV_DATA_INDEX_SPECVAL] = src_ep[VM_ENV_DATA_INDEX_SPECVAL];
+    RB_OBJ_WRITE(proc_obj, &ep[VM_ENV_DATA_INDEX_ENV], src_ep[VM_ENV_DATA_INDEX_ENV]);
 
     return proc_obj;
 }