[ios] pass --enable-monotouch to cross compilers so icall defintions …

…are visible to it (mono#12834)

This fixes a regression introduced by mono@5187b0b

The AOT compiler wasn't aware of the icalls since they are guarded by `ENABLE_MONOTOUCH`. Passing `--enable-monotouch` to configure of the AOT compiler enables that define, so it can properly resolve those icalls. However, to avoid `zlib` dependency for the cross compilers, we stub
them out.

mono/metadata/icall.c

@@ -7362,31 +7362,51 @@ G_EXTERN_C gint32   WriteZStream (gpointer stream, gpointer buffer, gint32 lengt
 gpointer
 ves_icall_System_IO_Compression_DeflateStreamNative_CreateZStream (gint32 compress, MonoBoolean gzip, gpointer feeder, gpointer data)
 {
+#ifdef MONO_CROSS_COMPILE
+	return NULL;
+#else
 	return CreateZStream (compress, gzip, feeder, data);
+#endif
 }
 
 gint32
 ves_icall_System_IO_Compression_DeflateStreamNative_CloseZStream (gpointer stream)
 {
+#ifdef MONO_CROSS_COMPILE
+	return 0;
+#else
 	return CloseZStream (stream);
+#endif
 }
 
 gint32
 ves_icall_System_IO_Compression_DeflateStreamNative_Flush (gpointer stream)
 {
+#ifdef MONO_CROSS_COMPILE
+	return 0;
+#else
 	return Flush (stream);
+#endif
 }
 
 gint32
 ves_icall_System_IO_Compression_DeflateStreamNative_ReadZStream (gpointer stream, gpointer buffer, gint32 length)
 {
+#ifdef MONO_CROSS_COMPILE
+	return 0;
+#else
 	return ReadZStream (stream, buffer, length);
+#endif
 }
 
 gint32
 ves_icall_System_IO_Compression_DeflateStreamNative_WriteZStream (gpointer stream, gpointer buffer, gint32 length)
 {
+#ifdef MONO_CROSS_COMPILE
+	return 0;
+#else
 	return WriteZStream (stream, buffer, length);
+#endif
 }
 
 #endif

sdks/builds/ios.mk

@@ -337,6 +337,7 @@ _ios-$(1)_CONFIGURE_FLAGS= \
 	--enable-dtrace=no \
 	--enable-icall-symbol-map \
 	--enable-minimal=com,remoting \
+	--enable-monotouch \
 	--disable-crash-reporting
 
 $$(eval $$(call CrossRuntimeTemplate,ios,$(1),$(2)-apple-darwin10,$(3)-darwin,$(4),$(5),$(6)))