Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_set_i32.c

@@ -0,0 +1,7 @@
+#include "tommath_private.h"
+#ifdef MP_SET_I32_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+MP_SET_SIGNED(mp_set_i32, mp_set_u32, int32_t, uint32_t)
+#endif