[rust] Add synstructure

Change-Id: I6e18adb4d78247bffd92c7c4e2facfed32b7df8b
diff --git a/rustc_deps/Cargo.lock b/rustc_deps/Cargo.lock
index 805134c..258e9b0 100644
--- a/rustc_deps/Cargo.lock
+++ b/rustc_deps/Cargo.lock
@@ -564,6 +564,7 @@
  "smallvec 0.6.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "structopt 0.2.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "syn 0.15.26 (registry+https://github.com/rust-lang/crates.io-index)",
+ "synstructure 0.10.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 3.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.42 (registry+https://github.com/rust-lang/crates.io-index)",
  "timebomb 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/rustc_deps/Cargo.toml b/rustc_deps/Cargo.toml
index 2ae303a..c97e8b6 100644
--- a/rustc_deps/Cargo.toml
+++ b/rustc_deps/Cargo.toml
@@ -71,6 +71,7 @@
 slab = "0.4"
 smallvec = "0.6"
 structopt = "0.2.14"
+synstructure = "0.10.1"
 tempfile = "3"
 time = "0.1"
 timebomb = "0.1.2"