gnutls: disable libtasn build for darwin

Change-Id: I715364bb626eff621bcd923e32f75a19dec03616

contrib/src/gnutls/rules.mak

@@ -42,7 +42,6 @@ GNUTLS_CONF := \
 	--disable-cxx \
 	--disable-srp-authentication \
 	--disable-psk-authentication-FIXME \
-	--with-included-libtasn1 \
 	--with-included-unistring \
 	--disable-openpgp-authentication \
 	--disable-openssl-compatibility \
@@ -53,6 +52,10 @@ GNUTLS_CONF := \
 	--without-idn \
 	$(HOSTCONF)
 
+ifndef HAVE_DARWIN_OS
+	GNUTLS_CONF += --with-included-libtasn1
+endif
+
 ifdef HAVE_IOS
 	GNUTLS_CONF += --disable-hardware-acceleration
 endif