Fix missing libc dependency used by backtrace-sys

Change-Id: I3f3eb037bba389ca7f5894a5d213eb99575357ef
diff --git a/rustc_deps/Cargo.lock b/rustc_deps/Cargo.lock
index 0270fc0..8039fb9 100644
--- a/rustc_deps/Cargo.lock
+++ b/rustc_deps/Cargo.lock
@@ -75,6 +75,9 @@
 [[package]]
 name = "backtrace-sys"
 version = "0.1.24"
+dependencies = [
+ "libc 0.2.43 (registry+https://github.com/rust-lang/crates.io-index)",
+]
 
 [[package]]
 name = "base64"
diff --git a/rustc_deps/tiny_mirrors/backtrace-sys/Cargo.toml b/rustc_deps/tiny_mirrors/backtrace-sys/Cargo.toml
index f440e71..b393649 100644
--- a/rustc_deps/tiny_mirrors/backtrace-sys/Cargo.toml
+++ b/rustc_deps/tiny_mirrors/backtrace-sys/Cargo.toml
@@ -7,3 +7,6 @@
 version = "0.1.24"
 authors = ["The Fuchsia Authors"]
 description = "A null replacement for the backtrace-sys crate"
+
+[dependencies]
+libc = "*"