Give clang one less thing to complain about

"s"[i<2] and "s" + (i<2) are literally identical, but the latter triggers
a warning from clang because it looks so much like a noob is trying to
concatenate an integer and a string.  The former is arguably more clear.

tcctools.c

@@ -390,7 +390,7 @@ usage:
     }
 
     if (v)
-        printf("<- %s (%d symbol%s)\n", outfile, i, "s" + (i<2));
+        printf("<- %s (%d symbol%s)\n", outfile, i, "s"[i<2]);
 
     ret = 0;