Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_cutoffs.c

@@ -0,0 +1,14 @@
+#include "tommath_private.h"
+#ifdef MP_CUTOFFS_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+#ifndef MP_FIXED_CUTOFFS
+#include "tommath_cutoffs.h"
+int MP_MUL_KARATSUBA_CUTOFF = MP_DEFAULT_MUL_KARATSUBA_CUTOFF,
+    MP_SQR_KARATSUBA_CUTOFF = MP_DEFAULT_SQR_KARATSUBA_CUTOFF,
+    MP_MUL_TOOM_CUTOFF = MP_DEFAULT_MUL_TOOM_CUTOFF,
+    MP_SQR_TOOM_CUTOFF = MP_DEFAULT_SQR_TOOM_CUTOFF;
+#endif
+
+#endif