use external for sane headers

Change-Id: I6fc53e185254a37df7d03ab6f91210b8e397db2e

RepositoryExternal.mk

@@ -126,6 +126,21 @@ endef
 
 endif
 
+ifeq (SANEUNX,$(filter SANE,$(BUILD_TYPE))$(GUI))
+
+define gb_LinkTarget__use_sane_headers
+$(call gb_Library_use_packages,$(1),\
+	sane_inc \
+)
+
+endef
+
+else
+
+gb_LinkTarget__use_sane_headers :=
+
+endif
+
 # External libraries
 
 ifeq ($(SYSTEM_CPPUNIT),YES)

extensions/Library_scn.mk

@@ -28,6 +28,10 @@
 
 $(eval $(call gb_Library_Library,scn))
 
+$(eval $(call gb_Library_use_externals,scn,\
+    sane_headers \
+))
+
 $(eval $(call gb_Library_set_componentfile,scn,extensions/source/scanner/scn))
 
 $(eval $(call gb_Library_use_sdk_api,scn))
@@ -56,9 +60,6 @@ $(eval $(call gb_Library_add_exception_objects,scn,\
 ))
 else
 ifeq ($(GUI),UNX)
-ifneq (,$(filter SANE,$(BUILD_TYPE)))
-$(eval $(call gb_Library_use_packages,scn,sane_inc))
-endif
 
 $(eval $(call gb_Library_add_exception_objects,scn,\
 	extensions/source/scanner/grid \