linux-user: define TARGET_ARCH_HAS_SETUP_FRAME

linux-user: define TARGET_ARCH_HAS_SETUP_FRAME

Instead of calling setup_frame() conditionally to a list of known targets,
define TARGET_ARCH_HAS_SETUP_FRAME if the target provides the function
and call it only if the macro is defined.

Move declarations of setup_frame() and setup_rt_frame() to
linux-user/signal-common.h

Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20180424192635.6027-21-laurent@vivier.eu>