Fix crash loading Swift symbol (I think associated with concurrency)

I add /usr/lib/swift as an rpath, which seems to fix the issue even though
there doesn't seem to be a relevant library at that location on my machine.

Based on my research, wondering if `-Wl,-weak-lswiftCompatibilityConcurrency`
is also required for this to work on older OSes, but holding back for now.

crates/zed/build.rs

@@ -15,6 +15,9 @@ fn main() {
         println!("cargo:rustc-link-arg=-Wl,-rpath,@executable_path");
     }
 
+    // Seems to be required to enable Swift concurrency
+    println!("cargo:rustc-link-arg=-Wl,-rpath,/usr/lib/swift");
+
     // Register exported Objective-C selectors, protocols, etc
     println!("cargo:rustc-link-arg=-Wl,-ObjC");