Add libjpeg and libpng to the Windows SDL LDFLAGS.

Theoretically, libjpeg shouldn't be necessary or used, but it needs to
be present at compile time on the Jenkins. I strongly suggest someone
look into how to get rid of that dependency without compiling a custom
sdl_image.
Merge pull request #2742 from narc0tiq/win32-tiles-libs

Add libjpeg and libpng to the Windows SDL LDFLAGS.