add freeype to cairo's use externals

Change-Id: I408c48ce0b28534b232b5d401ed13f7af76ed2ed
Reviewed-on: https://gerrit.libreoffice.org/33915Reviewed-by: Caolán McNamara <caolanm@redhat.com>
Tested-by: Caolán McNamara <caolanm@redhat.com>

external/cairo/ExternalProject_cairo.mk

@@ -12,6 +12,7 @@ $(eval $(call gb_ExternalProject_ExternalProject,cairo))
 $(eval $(call gb_ExternalProject_use_external_project,cairo,pixman))
 
 $(eval $(call gb_ExternalProject_use_externals,cairo,\
+	freetype \
 	png \
 	zlib \
 ))