Before

csc -C -I/usr/include/SDL -C -D_GNU_SOURCE=1 -C -D_REENTRANT -L -L/usr/lib/x86_64-linux-gnu -L -lSDL -L -lSDL_ttf -L -lSDL_image -L -lSDL_gfx -L -lSDL_net -s -o sdl.so sd
l.scm

(First -L does nothing, second -L sets the correct path, 3rd deletes the correct path, 3-nth do nothing).

After:

csc -C -I/usr/include/SDL -C -D_GNU_SOURCE=1 -C -D_REENTRANT -L/usr/lib/x86_64-linux-gnu -L -lSDL -lSDL_ttf -lSDL_image -lSDL_gfx -lSDL_net -s -o sdl.so sdl.scm