gnutls: re-enable gnutls-openssl compat library

This was disabled in the 3.4.x branch by default and is required by
inadyn, fixes:
http://autobuild.buildroot.net/results/51f/51f7e9275c2d23952c7558a126a8843d5476e4b1/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gnutls/gnutls.mk

@@ -17,6 +17,7 @@ GNUTLS_CONF_OPTS = \
 	--disable-libdane \
 	--disable-rpath \
 	--enable-local-libopts \
+	--enable-openssl-compatibility \
 	--with-libnettle-prefix=$(STAGING_DIR)/usr \
 	--with-librt-prefix=$(STAGING_DIR) \
 	--without-tpm