gdk_pixbuf_new_from_file_utf8 -- where it is defined?

[Stefan Salewski <mail ssalewski de>]

I am working on GTK3 wrappers/bindings for Nim language.

For gdk-pixbuf-2.31.2 there seems to exist a function
gdk_pixbuf_new_from_file_utf8 which is called in

gdk-pixbuf-io.c:
  retval = gdk_pixbuf_new_from_file_utf8 (utf8_filename, error);

and referenced in

gdk-pixbuf-core.h:
#define gdk_pixbuf_new_from_file gdk_pixbuf_new_from_file_utf8

Where is that function defined? Thanks.