Vendor dependencies

Let's see how I like this workflow.

vendor/parking_lot_core/build.rs

@@ -0,0 +1,10 @@
+// Automatically detect tsan in a way that's compatible with both stable (which
+// doesn't support sanitizers) and nightly (which does). Works because build
+// scripts gets `cfg` info, even if the cfg is unstable.
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+    let santizer_list = std::env::var("CARGO_CFG_SANITIZE").unwrap_or_default();
+    if santizer_list.contains("thread") {
+        println!("cargo:rustc-cfg=tsan_enabled");
+    }
+}