Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_log_n.c

@@ -0,0 +1,29 @@
+#include "tommath_private.h"
+#ifdef MP_LOG_N_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+mp_err mp_log_n(const mp_int *a, int base, int *c)
+{
+   if (mp_isneg(a) || mp_iszero(a) || (base < 2) || (unsigned)base > (unsigned)MP_DIGIT_MAX) {
+      return MP_VAL;
+   }
+
+   if (MP_HAS(S_MP_LOG_2EXPT) && MP_IS_2EXPT((mp_digit)base)) {
+      *c = s_mp_log_2expt(a, (mp_digit)base);
+      return MP_OKAY;
+   }
+
+   if (MP_HAS(S_MP_LOG_D) && (a->used == 1)) {
+      *c = s_mp_log_d((mp_digit)base, a->dp[0]);
+      return MP_OKAY;
+   }
+
+   if (MP_HAS(S_MP_LOG)) {
+      return s_mp_log(a, (mp_digit)base, c);
+   }
+
+   return MP_VAL;
+}
+
+#endif