Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_clear_multi.c

@@ -0,0 +1,18 @@
+#include "tommath_private.h"
+#ifdef MP_CLEAR_MULTI_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+#include <stdarg.h>
+
+void mp_clear_multi(mp_int *mp, ...)
+{
+   va_list args;
+   va_start(args, mp);
+   while (mp != NULL) {
+      mp_clear(mp);
+      mp = va_arg(args, mp_int *);
+   }
+   va_end(args);
+}
+#endif