gmodule: Add missing config #include to gmodule-deprecated.c

Otherwise it doesn’t know the value of `G_MODULE_IMPL`. Spotted by
`-Wundef`.

Signed-off-by: Philip Withnall <pwithnall@gnome.org>
diff --git a/gmodule/gmodule-deprecated.c b/gmodule/gmodule-deprecated.c
index 4827790..80dd340 100644
--- a/gmodule/gmodule-deprecated.c
+++ b/gmodule/gmodule-deprecated.c
@@ -1,4 +1,5 @@
 #include "config.h"
+#include "gmoduleconf.h"
 
 /* 
  * This is the only way to disable deprecation warnings for macros, and we need