tools/nolibc: Add statx() and make stat() rely on statx() if necessary

LoongArch and RISC-V 32-bit only have statx(). ARC, Hexagon, Nios2 and
OpenRISC have statx() and stat64() but not stat() or newstat(). Add
statx() and make stat() rely on statx() if necessary to make them happy.
We may just use statx() for all architectures in the future.

Signed-off-by: Feiyang Chen <chenfeiyang@loongson.cn>
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>