package/stunnel: doesn't build with libressl

Fix the following build failure with libressl:

In file included from tls.c:39:
prototypes.h:774:8: error: unknown type name 'CRYPTO_RWLOCK'
  774 | extern CRYPTO_RWLOCK *stunnel_locks[STUNNEL_LOCKS];
      |        ^~~~~~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/c48ba8e71dc917b2e11051088dd252be81b3609f

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/stunnel/Config.in

@@ -2,7 +2,8 @@ config BR2_PACKAGE_STUNNEL
 	bool "stunnel"
 	depends on BR2_USE_MMU # fork()
 	select BR2_PACKAGE_OPENSSL
-	select BR2_PACKAGE_LIBOPENSSL_ENABLE_DES if BR2_PACKAGE_LIBOPENSSL
+	select BR2_PACKAGE_OPENSSL_FORCE_LIBOPENSSL
+	select BR2_PACKAGE_LIBOPENSSL_ENABLE_DES
 	help
 	  Stunnel is a program that wraps any TCP connection with an SSL
 	  connection.