Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_clamp.c

@@ -0,0 +1,27 @@
+#include "tommath_private.h"
+#ifdef MP_CLAMP_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* trim unused digits
+ *
+ * This is used to ensure that leading zero digits are
+ * trimed and the leading "used" digit will be non-zero
+ * Typically very fast.  Also fixes the sign if there
+ * are no more leading digits
+ */
+void mp_clamp(mp_int *a)
+{
+   /* decrease used while the most significant digit is
+    * zero.
+    */
+   while ((a->used > 0) && (a->dp[a->used - 1] == 0u)) {
+      --(a->used);
+   }
+
+   /* reset the sign flag if zero */
+   if (mp_iszero(a)) {
+      a->sign = MP_ZPOS;
+   }
+}
+#endif