`-Z linker-flavor=ld.lld` broken since nightly-2018-06-29

[alecmocatta]

Per #39915, I've been using RUSTFLAGS=-Zlinker-flavor=ld.lld cargo build --target x86_64-unknown-linux-musl to, on my mac, compile for Linux. This broke when I upgraded recently.

alec$ RUSTFLAGS="-Z linker-flavor=ld.lld" cargo +nightly-2018-06-29 build --tests --verbose --target x86_64-unknown-linux-musl
       Fresh unicode-xid v0.1.0
       Fresh byteorder v1.2.3
       Fresh dtoa v0.4.3
       Fresh itoa v0.4.2
       Fresh proc-macro2 v0.4.6
       Fresh quote v0.6.3
       Fresh serde v1.0.70
       Fresh syn v0.14.4
       Fresh serde_json v1.0.22
       Fresh bincode v1.0.1
       Fresh serde_derive v1.0.70
       Fresh serde_closure v0.1.0 (file:///Users/alec/Documents/serde_closure)
    Finished dev [unoptimized + debuginfo] target(s) in 0.15s

alec$ RUSTFLAGS="-Z linker-flavor=ld.lld" cargo +nightly-2018-07-07 build --tests --verbose --target x86_64-unknown-linux-musl
       Fresh unicode-xid v0.1.0
       Fresh itoa v0.4.2
       Fresh byteorder v1.2.3
       Fresh dtoa v0.4.3
       Fresh proc-macro2 v0.4.6
       Fresh quote v0.6.3
       Fresh serde v1.0.70
       Fresh syn v0.14.4
       Fresh bincode v1.0.1
       Fresh serde_json v1.0.22
       Fresh serde_derive v1.0.70
   Compiling serde_closure v0.1.0 (file:///Users/alec/Documents/serde_closure)
     Running `rustc --crate-name serde_closure src/lib.rs --emit=dep-info,link -C debuginfo=2 --test -C metadata=da15495a1895345a -C extra-filename=-da15495a1895345a --out-dir /Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/deps --target x86_64-unknown-linux-musl -C incremental=/Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/incremental -L dependency=/Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/deps -L dependency=/Users/alec/Documents/serde_closure/target/debug/deps --extern bincode=/Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/deps/libbincode-25bfa2b23c4e50a1.rlib --extern serde=/Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/deps/libserde-863b31fb6448209f.rlib --extern serde_derive=/Users/alec/Documents/serde_closure/target/debug/deps/libserde_derive-fd090e5ae132a20a.dylib --extern serde_json=/Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/deps/libserde_json-f6c22624175f963f.rlib -Z linker-flavor=ld.lld`
error: linker `lld` not found====================================>     ] 13/14: serde_closure
  |
  = note: No such file or directory (os error 2)

error: aborting due to previous error

error: Could not compile `serde_closure`.

Caused by:
  process didn't exit successfully: `rustc --crate-name serde_closure src/lib.rs --emit=dep-info,link -C debuginfo=2 --test -C metadata=da15495a1895345a -C extra-filename=-da15495a1895345a --out-dir /Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/deps --target x86_64-unknown-linux-musl -C incremental=/Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/incremental -L dependency=/Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/deps -L dependency=/Users/alec/Documents/serde_closure/target/debug/deps --extern bincode=/Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/deps/libbincode-25bfa2b23c4e50a1.rlib --extern serde=/Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/deps/libserde-863b31fb6448209f.rlib --extern serde_derive=/Users/alec/Documents/serde_closure/target/debug/deps/libserde_derive-fd090e5ae132a20a.dylib --extern serde_json=/Users/alec/Documents/serde_closure/target/x86_64-unknown-linux-musl/debug/deps/libserde_json-f6c22624175f963f.rlib -Z linker-flavor=ld.lld` (exit code: 101)

[alexcrichton]

I believe this was caused by #51936 (cc @japaric) and can probably be fixed with -C linker=rust-lld

[alecmocatta]

@alexcrichton You're spot on, thank you! Apologies for missing that.

I'm now seeing a different error (rust-lld: error: unknown -z value: ,relro,-z,now) but I'll look further into it and create a new issue if appropriate.