Fix copy&paste error: check_long_long should check __builtin_ssubll_overflow

The constants are of the right type, but __builtin_ssubl_overflow was
used instead of __builtin_ssubll_overflow (which, however, made no
difference on 64-bit Linux platforms, which most of our tests run on).

Author: tautschnig

regression/cbmc/gcc_builtin_sub_overflow/main.c

@@ -26,10 +26,10 @@ void check_long(void)
 void check_long_long(void)
 {
   long result;
-  assert(!__builtin_ssubl_overflow(1ll, 1ll, &result));
+  assert(!__builtin_ssubll_overflow(1ll, 1ll, &result));
   assert(result == 0ll);
-  assert(__builtin_ssubl_overflow(LLONG_MIN, 1ll, &result));
-  assert(!__builtin_ssubl_overflow(LLONG_MIN / 2ll, LLONG_MAX / 2ll, &result));
+  assert(__builtin_ssubll_overflow(LLONG_MIN, 1ll, &result));
+  assert(!__builtin_ssubll_overflow(LLONG_MIN / 2ll, LLONG_MAX / 2ll, &result));
   assert(result - 1ll == LLONG_MIN);
   assert(0 && "reachability");
 }