Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_cmp_mag.c

@@ -0,0 +1,25 @@
+#include "tommath_private.h"
+#ifdef MP_CMP_MAG_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* compare maginitude of two ints (unsigned) */
+mp_ord mp_cmp_mag(const mp_int *a, const mp_int *b)
+{
+   int n;
+
+   /* compare based on # of non-zero digits */
+   if (a->used != b->used) {
+      return a->used > b->used ? MP_GT : MP_LT;
+   }
+
+   /* compare based on digits  */
+   for (n = a->used; n --> 0;) {
+      if (a->dp[n] != b->dp[n]) {
+         return a->dp[n] > b->dp[n] ? MP_GT : MP_LT;
+      }
+   }
+
+   return MP_EQ;
+}
+#endif