It was broken by commit 8ecc89f6 which
moved the SDL linker flags from macro libs_softmmu to macro SDL_LIBS.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Message-id: 20171116163732.31584-1-sw@weilnetz.de
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>