Actually use pkg-config to find libjpeg, and set cflags and ldflags for it.
Actually use pkg-config to find libjpeg, and set cflags and ldflags for it.

This makes the build work on DragonFly BSD, where libjpeg is usually found
in /usr/local/lib, so the existing fallback jpeg library detection failed
to specify the necessary -L library search path for linking.

ktossell/libuvc,ktossell/libuvc