chcon: link to libfts on musl targets

[ctrlcctrlv]

This fixes a build failure on aarch64-unknown-linux-musl.

On musl‐based targets the fts API is not provided by libc but by a separate libfts library.

src/uu/chcon/build.rs

Add a build script (build.rs) that detects when CARGO_CFG_TARGET_OS=linux && CARGO_CFG_TARGET_ENV=musl and emits rustc-link-lib=fts, so that uu_chcon can link successfully.

src/uu/chcon/src/fts.rs

In the glibc version of the header, level is short, under musl it's int; likewise, pathlen is unsigned on musl but signed on glibc.

Note

To test this, I build as: RUSTFLAGS='-Ctarget-feature=-crt-static' make in Alpine Linux.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/misc/stdbuf (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/misc/tee (passes in this run but fails in the 'main' branch)

[sylvestre]

i am not sure creating a build.rs is necessary

[ctrlcctrlv]

How else would you conditionally link the -lfts library?

[sylvestre]

not sure, sorry :)

[Ecordonnier]

@ctrlcctrlv Can you please clarify how you are building chcon with musl and selinux? I have tried with alpine linux arm64 docker image, but building selinux with musl is not a typical use-case, and I'm getting build errors because of missing libselinux etc.
The issue is that if we merge this PR, it would not be regression-tested by the existing CI setup (because feat_os_unix_musl does not contain feat_selinux in Cargo.toml).

I've tried this on my ubuntu x86 machine, but it doesn't work:

$ sudo apt install qemu-user-static
$ docker run --rm --privileged multiarch/qemu-user-static --reset -p yes
$ docker run --rm -it --platform linux/arm64   -v "$(pwd)":/work -w /work   rust:alpine sh

$ cat test-chcon-musl.sh 
#!/bin/sh
set -e

echo "=== Testing chcon musl ARM64 build ==="

echo "Architecture: $(uname -m)"

echo "Installing dependencies..."
apk add --no-cache musl-dev gcc make musl-fts-dev clang-dev clang-static llvm-static libselinux-dev libsepol-dev

echo ""
echo "Building chcon for musl (native build)..."
# Use static libclang for musl
export LIBCLANG_STATIC_PATH=/usr/lib/llvm21/lib
export RUSTY_LIBCLANG_LINK_STATIC=1
cargo build -p uu_chcon

echo ""
echo "Checking binary..."
ls -lh target/debug/chcon

echo ""
echo "Testing binary..."
./target/debug/chcon --help

echo ""
echo "✅ Build successful on musl ARM64 with SELinux and FTS!"

echo ""
echo "✅ Build successful!"

[Ecordonnier]

@ctrlcctrlv ping

[Ecordonnier]

Please reopen if you still want to continue working on it. I don't know how to test this, please see my comment above.