linux-user: disable qemu-bridge-helper and socket_scm_helper build

linux-user targets don't need them, and if we ask to build statically
linked binaries, some static libraries they need are not available.

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20180605160958.5434-1-laurent@vivier.eu>
2 files changed