XCALLOC is not used anywhere anymore, so it can be removed
diff --git a/tommath_private.h b/tommath_private.h
index 725aa4b..48cf37d 100644
--- a/tommath_private.h
+++ b/tommath_private.h
@@ -41,12 +41,10 @@ extern "C" {
# define XMALLOC malloc
# define XFREE free
# define XREALLOC realloc
-# define XCALLOC calloc
#else
/* prototypes for our heap functions */
extern void *XMALLOC(size_t n);
extern void *XREALLOC(void *p, size_t n);
-extern void *XCALLOC(size_t n, size_t s);
extern void XFREE(void *p);
#endif