linux-user: Add support for strace for statx() syscall

linux-user: Add support for strace for statx() syscall

All of the flags need to be conditional as old systems don't have
statx support.  Otherwise it works the same as other stat family
syscalls.  This requires the pending patch to add statx support.

Tested on Ubuntu 16.04 (no host statx) and Ubuntu 19.04 (with host
statx) using a riscv32-linux toolchain.

Signed-off-by: Jim Wilson <jimw@sifive.com>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Message-Id: <1561718618-20218-3-git-send-email-aleksandar.markovic@rt-rk.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>