three warnings building with gcc 10

---
insight.c: In function ‘status_enlightenment’:
insight.c:937:28: warning: ‘ (’ directive writing 2 bytes into a region of size between 0 and 255 [-Wformat-overflow=]
  937 |         Sprintf(buf, "%s %s (%s)", ustick ? "holding" : "held by",
      |                            ^~
In file included from ../include/config.h:631,
                 from ../include/hack.h:10,
                 from insight.c:15:
../include/global.h:274:24: note: ‘sprintf’ output 5 or more bytes (assuming 260) into a destination of size 256
  274 | #define Sprintf (void) sprintf
insight.c:937:9: note: in expansion of macro ‘Sprintf’
  937 |         Sprintf(buf, "%s %s (%s)", ustick ? "holding" : "held by",
      |         ^~~~~~~
insight.c:918:29: warning: ‘%s’ directive writing up to 255 bytes into a region of size 252 [-Wformat-overflow=]
  918 |         Sprintf(buf, "%s by %s",
      |                             ^~
  919 |                 is_animal(u.ustuck->data) ? "swallowed" : "engulfed",
  920 |                 heldmon);
      |                 ~~~~~~~
In file included from ../include/config.h:631,
                 from ../include/hack.h:10,
                 from insight.c:15:
../include/global.h:274:24: note: ‘sprintf’ output 5 or more bytes (assuming 260) into a destination of size 256
  274 | #define Sprintf (void) sprintf
insight.c:918:9: note: in expansion of macro ‘Sprintf’
  918 |         Sprintf(buf, "%s by %s",
      |         ^~~~~~~

---

zap.c:475:1: warning: old-style function definition [-Wold-style-definition]
  475 | release_hold()
      | ^~~~~~~~~~~~

src/insight.c

@@ -915,7 +915,7 @@ status_enlightenment(int mode, int final)
             Strcpy(heldmon, "an unseen creature");
     }
     if (u.uswallow) { /* implies u.ustuck is non-Null */
-        Sprintf(buf, "%s by %s",
+        Snprintf(buf, sizeof buf, "%s by %s",
                 is_animal(u.ustuck->data) ? "swallowed" : "engulfed",
                 heldmon);
         if (dmgtype(u.ustuck->data, AD_DGST)) {
@@ -934,8 +934,9 @@ status_enlightenment(int mode, int final)
         boolean ustick = (Upolyd && sticks(g.youmonst.data));
         int dx = u.ustuck->mx - u.ux, dy = u.ustuck->my - u.uy;
 
-        Sprintf(buf, "%s %s (%s)", ustick ? "holding" : "held by",
+        Snprintf(buf, sizeof buf, "%s %s (%s)",
-                heldmon, dxdy_to_dist_descr(dx, dy, TRUE));
+                 ustick ? "holding" : "held by",
+                 heldmon, dxdy_to_dist_descr(dx, dy, TRUE));
         you_are(buf, "");
     }
     if (Riding) {

src/zap.c

@@ -472,7 +472,7 @@ bhitm(struct monst *mtmp, struct obj *otmp)
 /* hero is held by a monster or engulfed or holding a monster and has zapped
    opening/unlocking magic at holder/engulfer/holdee or at self */
 void
-release_hold()
+release_hold(void)
 {
     struct monst *mtmp = u.ustuck;