Don't use function definitions looking like old-style ones.

This fixes a bunch of somewhat pedantic warnings with new
compilers. Since by far the majority of other functions definitions use
the (void) style it just seems to be consistent to do so as well in the
remaining few places.

src/backend/utils/time/snapmgr.c

@@ -345,7 +345,7 @@ GetNonHistoricCatalogSnapshot(Oid relid)
  * cycles we spent tracking such fine details would be well-spent.
  */
 void
-InvalidateCatalogSnapshot()
+InvalidateCatalogSnapshot(void)
 {
 	CatalogSnapshotStale = true;
 }