Set up to build Rust code with dependencies

cargo-raze is like gazelle, but for Rust code. It generates BUILD files
for external dependencies.

I'm putting this in a separate change from running it and setting up CI
to do that for ease of telling what's generated vs not.

Change-Id: I87a07255dca475514cae7bdbf9b0b62ce46e2512
Signed-off-by: Brian Silverman <bsilver16384@gmail.com>
diff --git a/third_party/bazel-toolchain/toolchain/BUILD.llvm_repo b/third_party/bazel-toolchain/toolchain/BUILD.llvm_repo
index 9920705..c0dbadf 100644
--- a/third_party/bazel-toolchain/toolchain/BUILD.llvm_repo
+++ b/third_party/bazel-toolchain/toolchain/BUILD.llvm_repo
@@ -124,3 +124,8 @@
     name = "strip",
     srcs = ["bin/llvm-strip"],
 )
+
+filegroup(
+    name = "libclang",
+    srcs = ["lib/libclang.so"],
+)