Add SYS_FRETURNFD, xopen, and xdup.

3 jobs for cross_scheme_links in 1 minute and 8 seconds (queued for 2 seconds)
latest
Name Stage Failure
failed
build:redox Build
Some errors have detailed explanations: E0432, E0658.
For more information about an error, try `rustc --explain E0432`.
error: could not compile `redox_syscall`

Caused by:
process didn't exit successfully: `rustc --crate-name syscall --edition=2018 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 -C metadata=27081be3baa2250b -C extra-filename=-27081be3baa2250b --out-dir /builds/4lDO2/syscall/target/x86_64-unknown-redox/debug/deps --target x86_64-unknown-redox -C linker=x86_64-unknown-redox-gcc -C incremental=/builds/4lDO2/syscall/target/x86_64-unknown-redox/debug/incremental -L dependency=/builds/4lDO2/syscall/target/x86_64-unknown-redox/debug/deps -L dependency=/builds/4lDO2/syscall/target/debug/deps --extern bitflags=/builds/4lDO2/syscall/target/x86_64-unknown-redox/debug/deps/libbitflags-c7e00a063f3f73ab.rmeta -L /root/.redoxer/toolchain/x86_64-unknown-redox/lib` (exit status: 1)
redoxer cargo: exit status: 101
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1

failed
build:linux Build

Some errors have detailed explanations: E0432, E0658.
For more information about an error, try `rustc --explain E0432`.
error: could not compile `redox_syscall` due to 7 previous errors; 4 warnings emitted

Caused by:
process didn't exit successfully: `rustc --crate-name syscall --edition=2018 src/lib.rs --error-format=json --json=diagnostic-rendered-ansi --crate-type lib --emit=dep-info,metadata,link -C embed-bitcode=no -C debuginfo=2 -C metadata=036765bea450d06b -C extra-filename=-036765bea450d06b --out-dir /builds/4lDO2/syscall/target/debug/deps -C incremental=/builds/4lDO2/syscall/target/debug/incremental -L dependency=/builds/4lDO2/syscall/target/debug/deps --extern bitflags=/builds/4lDO2/syscall/target/debug/deps/libbitflags-98add49f7789fc8a.rmeta` (exit status: 1)
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1