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/ignore.c

@@ -271,7 +271,7 @@ ignore_read_next_entry (char *my_cfg, struct ignore *ignore)
 }
 
 void
-ignore_load ()
+ignore_load (void)
 {
 	struct ignore *ignore;
 	struct stat st;
@@ -302,7 +302,7 @@ ignore_load ()
 }
 
 void
-ignore_save ()
+ignore_save (void)
 {
 	char buf[1024];
 	int fh;