Fix MSVC build

Have to pass AR=lib.exe and SED=sed.exe on the configure command line,
otherwise for some reason it doesn't know what archiver to use, and
thinks it can't find a sed that does not truncate output.

Change-Id: I1ce211119e62b6ecf6a2fc8fc89cdde2c7bb985a

libwpg/ExternalProject_libwpg.mk

@@ -30,6 +30,7 @@ $(call gb_ExternalProject_get_state_target,libwpg,build) :
 			--disable-debug \
 			--disable-werror \
 			$(if $(filter YES,$(CROSS_COMPILING)),--build=$(BUILD_PLATFORM) --host=$(HOST_PLATFORM)) \
+			$(if $(filter MSC,$(COM)),AR=lib.exe SED=sed.exe) \
 		&& (cd $(EXTERNAL_WORKDIR)/src/lib && $(MAKE)) \
 	)