Rollup merge of #136213 - erickt:fs, r=Mark-Simulacrum

Allow Rust to use a number of libc filesystem calls

This allows Rust on Fuchsia to use a number of function calls from libc:

* dirfd
* fdatasync
* flock with LOCK_EX, LOCK_SH, LOCK_NB, LOCK_UN
* fstatat

cc #120426

try-job: dist-various-2

Author: Urgau