Don't mix declarations and code (not widely portable).

client/mysqltest.c:
  Don't mix declarations and code.
  Tid up function code.

client/mysqltest.c

@@ -1329,38 +1329,43 @@ static int run_tool(const char *tool_path, DYNAMIC_STRING *ds_res, ...)
   DBUG_RETURN(ret);
 }
 
+
 /*
   Test if diff is present.  This is needed on Windows systems
   as the OS returns 1 whether diff is successful or if it is
   not present.
-  
+
   We run diff -v and look for output in stdout.
   We don't redirect stderr to stdout to make for a simplified check
   Windows will output '"diff"' is not recognized... to stderr if it is
   not present.
 */
 
-int diff_check(const char *diff_name)
+#ifdef __WIN__
+
+static int diff_check(const char *diff_name)
 {
-  char buf[512]= {0};
   FILE *res_file;
-  char cmd[128];
-  my_snprintf (cmd, sizeof(cmd), "%s -v", diff_name);
-  int have_diff = 0;
+  char buf[128];
+  int have_diff= 0;
 
-  if (!(res_file= popen(cmd, "r")))
-    die("popen(\"%s\", \"r\") failed", cmd);
+  my_snprintf(buf, sizeof(buf), "%s -v", diff_name);
 
-  /* if diff is not present, nothing will be in
-   * stdout to increment have_diff */
+  if (!(res_file= popen(buf, "r")))
+    die("popen(\"%s\", \"r\") failed", buf);
+
+  /* if diff is not present, nothing will be in stdout to increment have_diff */
   if (fgets(buf, sizeof(buf), res_file))
-  {
-    have_diff += 1;
-  } 
+    have_diff= 1;
+
   pclose(res_file);
+
   return have_diff;
 }
 
+#endif
+
+
 /*
   Show the diff of two files using the systems builtin diff
   command. If no such diff command exist, just dump the content