Auto merge of #1577 - oxalica:statx-syscall, r=gnzlbg

Provide SYS_statx for more target_arch/target_env

Fixes #1545

The syscall `statx` is provided by Linux Kernel, so it should be available on any `target_env`/`target_arch`, not only some arch on `gnu`.

Syscall ids are got from [this commit of musl](http://git.etalabs.net/cgit/musl/commit/?id=9864f60e929100e253fc813bd4105d6dd7652787), except for hexagon, which is got from Linux Kernel (`make O=build ARCH=hexagon headers`).

**Not tested yet**