fix some libnh wasm build issues

emcc: error: linker setting ignored during compilation: 'ASSERTIONS' [-Wunused-command-line-argument] [-Werror]
make[1]: *** [Makefile:1306: ../targets/wasm/allmain.o] Error 1

wasm-ld: error: ../targets/wasm/version.o: undefined symbol: nomakedefs

These ones look like actual NetHack issues that this particular compile is catching due to
default -Wunused-but-set-variable.

In the interest of time today, I mostly resorted to using nhUse() on them for now, but a
follow-up by someone might be useful.

options.c:6069:13: error: variable 'ret' set but not used [-Werror,-Wunused-but-set-variable]
    boolean ret = FALSE;
            ^

restore.c:903:9: error: variable 'len' set but not used [-Werror,-Wunused-but-set-variable]
    int len = 0;
        ^

uhitm.c:4539:43: error: variable 'nsum' set but not used [-Werror,-Wunused-but-set-variable]
    int i, tmp, armorpenalty, sum[NATTK], nsum = MM_MISS,
                                          ^

src/options.c

@@ -6074,6 +6074,8 @@ parsebindings(char *bindings)
         ret |= parsebindings(bind);
     }
 
+    nhUse(ret);
+    
     /* parse a single binding: first split around : */
     if (! (bind = index(bindings, ':')))
         return FALSE; /* it's not a binding */

src/restore.c

@@ -927,6 +927,7 @@ rest_stairs(NHFILE* nhfp)
         if (newst)
             newst->u_traversed = stway.u_traversed;
     }
+    nhUse(len);    /* unclear why this variable exists though */
 }
 
 void

src/uhitm.c

@@ -4541,6 +4541,13 @@ hmonas(struct monst *mon)
     int dieroll, multi_claw = 0;
     boolean monster_survived;
 
+    /* FIXME: One compiler was getting a fatal 
+       variable nsum set but not used [-Werror,-Wunused-but-set-variable]
+       For now, I'm working around it with nhUse() but it should be
+       investigated when someone has the time.
+     */
+    nhUse(nsum);
+
     /* not used here but umpteen mhitm_ad_xxxx() need this */
     g.vis = (canseemon(mon) || distu(mon->mx, mon->my) <= 2);