Add exported libsudo_util functions to util.exp and mark in headers

using __dso_public.

lib/util/regress/fnmatch/fnm_test.c

@@ -14,14 +14,15 @@
 #ifdef HAVE_STRINGS_H
 # include <strings.h>
 #endif /* HAVE_STRINGS_H */
+
+#include "missing.h"
+
 #ifdef HAVE_FNMATCH
 # include <fnmatch.h>
 #else
 # include "compat/fnmatch.h"
 #endif
 
-#include "missing.h"
-
 __dso_public int main(int argc, char *argv[]);
 
 int