Fix function prototypes for list of arguments

At the moment, building WeeChat triggers several thousand -Wstrict-prototypes
diagnostics.  This is due to its source code using an empty argument list for
functions and function pointers that take no arguments, instead of explicitly
declaring that they take no arguments by using a void list.

This commit replaces all empty argument lists with a void list.

Note that Ruby's headers also suffer the same problem, which WeeChat can't
do anything to fix.  Thus, building WeeChat with the Ruby plugin enabled
will still issue approximately 30 such diagnostics.

src/core/core-debug.c

@@ -93,7 +93,7 @@ long long debug_long_callbacks = 0;    /* callbacks taking more than        */
  */
 
 void
-debug_build_info ()
+debug_build_info (void)
 {
     /* display version and compilation date/time */
     string_fprintf (
@@ -343,7 +343,7 @@ debug_windows_tree_display (struct t_gui_window_tree *tree, int indent)
  */
 
 void
-debug_windows_tree ()
+debug_windows_tree (void)
 {
     gui_chat_printf (NULL, "");
     gui_chat_printf (NULL, _("Windows tree:"));
@@ -355,7 +355,7 @@ debug_windows_tree ()
  */
 
 void
-debug_memory ()
+debug_memory (void)
 {
 #ifdef HAVE_MALLINFO2
     struct mallinfo2 info;
@@ -501,7 +501,7 @@ debug_hdata_map_cb (void *data,
  */
 
 void
-debug_hdata ()
+debug_hdata (void)
 {
     int count;
 
@@ -519,7 +519,7 @@ debug_hdata ()
  */
 
 void
-debug_hooks ()
+debug_hooks (void)
 {
     int i;
 
@@ -653,7 +653,7 @@ debug_hooks_plugin_types (const char *plugin_mask, const char **hook_types)
  */
 
 void
-debug_infolists ()
+debug_infolists (void)
 {
     struct t_infolist *ptr_infolist;
     struct t_infolist_item *ptr_item;
@@ -817,7 +817,7 @@ debug_libs_cb (const void *pointer, void *data,
  */
 
 void
-debug_directories ()
+debug_directories (void)
 {
     char *extra_libdir, str_temp[1024];
 
@@ -1026,7 +1026,7 @@ debug_unicode (const char *string)
  */
 
 void
-debug_init ()
+debug_init (void)
 {
     /*
      * hook signals with high priority, to be sure they will be used before
@@ -1042,6 +1042,6 @@ debug_init ()
  */
 
 void
-debug_end ()
+debug_end (void)
 {
 }