Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_copy.c

@@ -0,0 +1,29 @@
+#include "tommath_private.h"
+#ifdef MP_COPY_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* copy, b = a */
+mp_err mp_copy(const mp_int *a, mp_int *b)
+{
+   mp_err err;
+
+   /* if dst == src do nothing */
+   if (a == b) {
+      return MP_OKAY;
+   }
+
+   /* grow dest */
+   if ((err = mp_grow(b, a->used)) != MP_OKAY) {
+      return err;
+   }
+
+   /* copy everything over and zero high digits */
+   s_mp_copy_digs(b->dp, a->dp, a->used);
+   s_mp_zero_digs(b->dp + a->used, b->used - a->used);
+   b->used = a->used;
+   b->sign = a->sign;
+
+   return MP_OKAY;
+}
+#endif