Makefile.vc: fix webp_quality.exe link

when building a dll based libwebp include the dsp private symbols that
WebPUnmultiplyARGB requires

Change-Id: I7cf7da0b20d6cf6740219c8562380926a0abd93c
(cherry picked from commit cf047e8347314937435aabe643cf2fee0aa4a55b)
1 file changed