fix windows build(external/poppler)

Fix build error on windows with --enable-dbgutil autogen.sh option.
We need to link freetype248_D.lib,when we use --enable-dbgutil option.
(Suffix "_D" is needed.)

Change-Id: Ib2927e777d9b9bb615e1df62e428cf17cc8bc26e
Reviewed-on: https://gerrit.libreoffice.org/9248
Tested-by: Michael Stahl <mstahl@redhat.com>
Reviewed-by: Michael Stahl <mstahl@redhat.com>