tsearch.3: Use size_t for malloc() argument

Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man3/tsearch.3

@@ -271,6 +271,7 @@ in order.
 .EX
 #define _GNU_SOURCE     /* Expose declaration of tdestroy() */
 #include <search.h>
+#include <stddef.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <time.h>
@@ -278,7 +279,7 @@ in order.
 static void *root = NULL;
 
 static void *
-xmalloc(unsigned n)
+xmalloc(size_t n)
 {
     void *p;
     p = malloc(n);