g_thread_init: take a gpointer as the arg

GThreadFunctions is about to disappear.

glib/gthread.h

@@ -158,7 +158,7 @@ GLIB_VAR guint64   (*g_thread_gettime) (void);
  * only be called once, and must not be called directly or indirectly
  * from another glib-function, e.g. as a callback.
  */
-void    g_thread_init   (GThreadFunctions       *vtable);
+void    g_thread_init   (gpointer vtable);
 
 /* Checks if thread support is initialized.  Identical to the
  * g_thread_supported macro but provided for language bindings.

gthread/gthread-impl.c

@@ -36,7 +36,7 @@
 #include "gthreadprivate.h"
 
 void
-g_thread_init (GThreadFunctions *init)
+g_thread_init (gpointer init)
 {
   static gboolean already_done;
 
@@ -52,7 +52,7 @@ g_thread_init (GThreadFunctions *init)
 }
 
 void
-g_thread_init_with_errorcheck_mutexes (GThreadFunctions *vtable)
+g_thread_init_with_errorcheck_mutexes (gpointer vtable)
 {
   g_assert (vtable == NULL);