Try to manage without curl on non-desktop platforms (iOS, for me)

We don't build curl for iOS. (Don't remember why exactly, but anyway,
this persona thing is surely a feature relevant for desktop platforms
only, and certainly not a good reason to start building curl.)

Change-Id: Ia2acebe77a0acb9dbf5858e6524c444e772ac8c8
Reviewed-on: https://gerrit.libreoffice.org/61520
Tested-by: Jenkins
Reviewed-by: Tor Lillqvist <tml@collabora.com>

cui/Library_cui.mk

@@ -66,7 +66,8 @@ $(eval $(call gb_Library_use_externals,cui,\
 	boost_headers \
 	$(call gb_Helper_optional,OPENCL,\
 		clew) \
-    curl \
+    $(call gb_Helper_optional,DESKTOP,\
+		curl) \
     icuuc \
     icu_headers \
     orcus-parser \
@@ -174,7 +175,8 @@ $(eval $(call gb_Library_add_exception_objects,cui,\
     cui/source/options/optpath \
     cui/source/options/optsave \
     cui/source/options/optupdt \
-    cui/source/options/personalization \
+    $(call gb_Helper_optional,DESKTOP,\
+        cui/source/options/personalization) \
     cui/source/options/personasdochandler \
     cui/source/options/radiobtnbox \
     cui/source/options/sdbcdriverenum \