Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_get_l.c

@@ -0,0 +1,7 @@
+#include "tommath_private.h"
+#ifdef MP_GET_L_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+MP_GET_SIGNED(mp_get_l, mp_get_mag_ul, long, unsigned long)
+#endif