When generating the trace/generated-ust.c source file, make sure
it includes osdep.h as its first include.

This fixes compilation with --enable-trace-backends=ust
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Message-id: 1456240661-15422-1-git-send-email-peter.maydell@linaro.org
Reviewed-by: NEric Blake <eblake@redhat.com>