musl-fts: setup-hook to add -lfts, use in xar and libselinux

[dtzWill]

libselinux and friends need updates to work w/musl
(I have fixes to current versions but #36978
is the way to go and is hopefully merged soon)

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.

---

[GrahamcOfBorg]

Success on x86_64-linux (full log)

Attempted: libselinux, musl-fts, xar

Partial log (click to expand)

post-installation fixup
shrinking RPATHs of ELF executables and libraries in /nix/store/ixhrn6l83imws0lp5d7svapzbi1ni7wa-musl-fts-2017-01-13
shrinking /nix/store/ixhrn6l83imws0lp5d7svapzbi1ni7wa-musl-fts-2017-01-13/lib/libfts.so.0.0.0
strip is /nix/store/j75dgadrff2d1fyc4fczmcgqkid2imdx-binutils-2.30/bin/strip
stripping (with command strip and flags -S) in /nix/store/ixhrn6l83imws0lp5d7svapzbi1ni7wa-musl-fts-2017-01-13/lib
patching script interpreter paths in /nix/store/ixhrn6l83imws0lp5d7svapzbi1ni7wa-musl-fts-2017-01-13
checking for references to /build in /nix/store/ixhrn6l83imws0lp5d7svapzbi1ni7wa-musl-fts-2017-01-13...
/nix/store/h69csf8khs9k6pfb2qspcgazx0rxsh68-libselinux-2.4
/nix/store/ixhrn6l83imws0lp5d7svapzbi1ni7wa-musl-fts-2017-01-13
/nix/store/xh9jm8221abk44l365g518446y6hicvl-xar-1.6.1

[GrahamcOfBorg]

Success on aarch64-linux (full log)

Attempted: libselinux, musl-fts, xar

Partial log (click to expand)

shrinking /nix/store/jx7gshl0f39rl94qy1kbjglxrn4aslf6-xar-1.6.1/bin/xar
shrinking /nix/store/jx7gshl0f39rl94qy1kbjglxrn4aslf6-xar-1.6.1/lib/libxar.so.1
gzipping man pages under /nix/store/jx7gshl0f39rl94qy1kbjglxrn4aslf6-xar-1.6.1/share/man/
strip is /nix/store/j7d4mr0ikv974ig7yzhknpsq288js4bs-binutils-2.30/bin/strip
stripping (with command strip and flags -S) in /nix/store/jx7gshl0f39rl94qy1kbjglxrn4aslf6-xar-1.6.1/lib  /nix/store/jx7gshl0f39rl94qy1kbjglxrn4aslf6-xar-1.6.1/bin
patching script interpreter paths in /nix/store/jx7gshl0f39rl94qy1kbjglxrn4aslf6-xar-1.6.1
checking for references to /build in /nix/store/jx7gshl0f39rl94qy1kbjglxrn4aslf6-xar-1.6.1...
/nix/store/agsps25jc7cv6sgdkx2mm3b94vih8zi1-libselinux-2.4
/nix/store/dp7f4dcppr6q2fih46dxbn8y60d574r8-musl-fts-2017-01-13
/nix/store/jx7gshl0f39rl94qy1kbjglxrn4aslf6-xar-1.6.1

[GrahamcOfBorg]

Success on x86_64-darwin (full log)

Attempted: musl-fts, xar

The following builds were skipped because they don't evaluate on x86_64-darwin: libselinux

Partial log (click to expand)

 /nix/store/b77377767pk2fyw5yz2x6lwh0i84z84m-coreutils-8.29/bin/install -c -m 644 fts.h '/nix/store/hm4vzc0i7i5yx2i1h9fwh8vxxk50jyh7-musl-fts-2017-01-13/include'
 /nix/store/b77377767pk2fyw5yz2x6lwh0i84z84m-coreutils-8.29/bin/mkdir -p '/nix/store/hm4vzc0i7i5yx2i1h9fwh8vxxk50jyh7-musl-fts-2017-01-13/lib/pkgconfig'
 /nix/store/b77377767pk2fyw5yz2x6lwh0i84z84m-coreutils-8.29/bin/install -c -m 644 musl-fts.pc '/nix/store/hm4vzc0i7i5yx2i1h9fwh8vxxk50jyh7-musl-fts-2017-01-13/lib/pkgconfig'
make[1]: Leaving directory '/private/tmp/nix-build-musl-fts-2017-01-13.drv-0/source'
post-installation fixup
strip is /nix/store/5fc1zygrlgfdzkfk1hajdw81czs5v9y9-cctools-binutils-darwin/bin/strip
stripping (with command strip and flags -S) in /nix/store/hm4vzc0i7i5yx2i1h9fwh8vxxk50jyh7-musl-fts-2017-01-13/lib
patching script interpreter paths in /nix/store/hm4vzc0i7i5yx2i1h9fwh8vxxk50jyh7-musl-fts-2017-01-13
/nix/store/hm4vzc0i7i5yx2i1h9fwh8vxxk50jyh7-musl-fts-2017-01-13
/nix/store/rn78g8xjk0pq1ydxqwvgilwfq33i2655-xar-1.6.1