Fix clang -Wstrict-prototypes warnings

This trivial diff gets rid of noisy warnings such as
```
./src/common/ignore.c:274:13: warning: a function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]
  274 | ignore_load ()
      |             ^
      |              void
```
when building with modern clang. This is cosmetic since these functions
are actually prototyped in a header, so if the header is in scope it's
not possible to call them with an arbitrary number of arguments.

src/common/text.c

@@ -1808,7 +1808,7 @@ pevent_check_all_loaded (void)
 }
 
 void
-load_text_events ()
+load_text_events (void)
 {
 	memset (&pntevts_text, 0, sizeof (char *) * (NUM_XP));
 	memset (&pntevts, 0, sizeof (char *) * (NUM_XP));
@@ -2488,7 +2488,7 @@ sound_load_event (char *evt, char *file)
 }
 
 void
-sound_load ()
+sound_load (void)
 {
 	int fd;
 	char buf[512];
@@ -2521,7 +2521,7 @@ sound_load ()
 }
 
 void
-sound_save ()
+sound_save (void)
 {
 	int fd, i;
 	char buf[512];