Fix namespace_initialize to not crash on boot

```
/opt/rubies/head-namespaces/bin/ruby(sigsegv+0x84) [0x104e897e8]
/usr/lib/system/libsystem_platform.dylib(_sigtramp+0x38) [0x18de56de4]
/opt/rubies/head-namespaces/bin/ruby(object_id+0x80) [0x104d7d420]
/opt/rubies/head-namespaces/bin/ruby(object_id+0x80) [0x104d7d420]
/opt/rubies/head-namespaces/bin/ruby(rb_initialize_main_namespace+0xe4) [0x104ddaa20]
/opt/rubies/head-namespaces/bin/ruby(ruby_opt_init+0x120) [0x104e7f524]
/opt/rubies/head-namespaces/bin/ruby(ruby_process_options+0x1370) [0x104e7e31c]
/opt/rubies/head-namespaces/bin/ruby(ruby_options+0xb0) [0x104d69844]
/opt/rubies/head-namespaces/bin/ruby(main+0x64) [0x104ca8d54]
```

I'm not too sure why `rb_obj_id` crashes, but I suspect it's called too
early. Either way I don't think generating an object_id for namespaces
is a good idea. If all we need is a unique number we can do that
for much cheaper.

Author: byroot

namespace.c

@@ -378,6 +378,20 @@ rb_current_namespace_details(VALUE opt)
     return str;
 }
 
+static long namespace_id_counter = 0;
+
+static long
+namespace_generate_id(void)
+{
+    long id;
+    RB_VM_LOCK_ENTER();
+    {
+        id = ++namespace_id_counter;
+    }
+    RB_VM_LOCK_LEAVE();
+    return id;
+}
+
 static void
 namespace_entry_initialize(rb_namespace_t *ns)
 {
@@ -527,7 +541,7 @@ namespace_initialize(VALUE namespace)
     ns = get_namespace_struct_internal(entry);
 
     ns->ns_object = namespace;
-    ns->ns_id = NUM2LONG(rb_obj_id(namespace));
+    ns->ns_id = namespace_generate_id();
     ns->load_path = rb_ary_dup(GET_VM()->load_path);
     ns->is_user = true;
     rb_define_singleton_method(ns->load_path, "resolve_feature_path", rb_resolve_feature_path, 1);
@@ -981,7 +995,7 @@ rb_initialize_main_namespace(void)
     main_ns = rb_class_new_instance_pass_kw(0, NULL, rb_cNamespace);
     ns = rb_get_namespace_t(main_ns);
     ns->ns_object = main_ns;
-    ns->ns_id = NUM2LONG(rb_obj_id(main_ns));
+    ns->ns_id = namespace_generate_id();
     ns->is_builtin = false;
     ns->is_user = true;
     ns->is_optional = false;