Missing dylib error in tests of plugin crate

[sfackler]

rls-preview 0.128.0-nightly (3e3df04 2018-05-16)

Running nightly RLS on the phf repo results in errors in the tests and benchmarks of the compiler plugin crate:

plugin `phf_macros` only found in rlib format, but must be available in dylib format

https://github.com/sfackler/rust-phf

[nrc]

The Cargo.toml has plugin = true which should cause Cargo to emit a dylib rather than an rlib, but in the RLS this seems not to happen. I think this will only affect programs using 'old' proc macros.

[nrc]

Note for self, correct command line:

rustc --crate-name phf_macros phf_macros/src/lib.rs --crate-type dylib --emit=dep-info,link -C prefer-dynamic -C debuginfo=2 -C metadata=4cc3765a8491e8fa --out-dir /Users/nick/version-controlled/rust-phf/target/debug/deps -C incremental=/Users/nick/version-controlled/rust-phf/target/debug/incremental -L dependency=/Users/nick/version-controlled/rust-phf/target/debug/deps --extern phf_generator=/Users/nick/version-controlled/rust-phf/target/debug/deps/libphf_generator-eb9d9deadb6e6691.rlib --extern phf_shared=/Users/nick/version-controlled/rust-phf/target/debug/deps/libphf_shared-79716c11db71145b.rlib

Note: --crate-type dylib