ios: build gnutls

Keychain patch is not iOS compatible.
See here:
https://mailman.videolan.org/pipermail/vlc-commits/2013-November/022795.html

Tuleap: #313
Change-Id: I9dfb7a385bb4e2ecafdd58ce675c14c251302738

contrib/src/gnutls/rules.mak

@@ -28,7 +28,9 @@ endif
 #endif
 	$(APPLY) $(SRC)/gnutls/gnutls-no-egd.patch
 	$(APPLY) $(SRC)/gnutls/read-file-limits.h.patch
+ifndef HAVE_IOS
 	$(APPLY) $(SRC)/gnutls/mac-keychain-lookup.patch
+endif
 	$(APPLY) $(SRC)/gnutls/format-security.patch
 	$(call pkg_static,"lib/gnutls.pc.in")
 	$(UPDATE_AUTOCONFIG)