Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_div.c

@@ -0,0 +1,42 @@
+#include "tommath_private.h"
+#ifdef MP_DIV_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+mp_err mp_div(const mp_int *a, const mp_int *b, mp_int *c, mp_int *d)
+{
+   mp_err err;
+
+   /* is divisor zero ? */
+   if (mp_iszero(b)) {
+      return MP_VAL;
+   }
+
+   /* if a < b then q = 0, r = a */
+   if (mp_cmp_mag(a, b) == MP_LT) {
+      if (d != NULL) {
+         if ((err = mp_copy(a, d)) != MP_OKAY) {
+            return err;
+         }
+      }
+      if (c != NULL) {
+         mp_zero(c);
+      }
+      return MP_OKAY;
+   }
+
+   if (MP_HAS(S_MP_DIV_RECURSIVE)
+       && (b->used > (2 * MP_MUL_KARATSUBA_CUTOFF))
+       && (b->used <= ((a->used/3)*2))) {
+      err = s_mp_div_recursive(a, b, c, d);
+   } else if (MP_HAS(S_MP_DIV_SCHOOL)) {
+      err = s_mp_div_school(a, b, c, d);
+   } else if (MP_HAS(S_MP_DIV_SMALL)) {
+      err = s_mp_div_small(a, b, c, d);
+   } else {
+      err = MP_VAL;
+   }
+
+   return err;
+}
+#endif