Change preprocessor tests to match what we will be using.

mysys/my_symlink.c

@@ -109,7 +109,7 @@ int my_symlink(const char *content, const char *linkname, myf MyFlags)
 
 int my_is_symlink(const char *filename __attribute__((unused)))
 {
-#if defined(HAVE_REALPATH) && !defined(HAVE_purify) && !defined(HAVE_BROKEN_REALPATH)
+#if defined(HAVE_LSTAT) && defined(S_ISLNK)
   struct stat stat_buff;
   return !lstat(filename, &stat_buff) && S_ISLNK(stat_buff.st_mode);
 #else