rustc: Change LLVM target for the wasm32-wasip2 Rust target

This commit changes the LLVM target of for the Rust `wasm32-wasip2`
target to `wasm32-wasip2` as well. LLVM does a bit of detection on the
target string to know when to call `wasm-component-ld` vs `wasm-ld` so
otherwise clang is invoking the wrong linker.

compiler/rustc_target/src/spec/targets/wasm32_wasip2.rs

@@ -55,7 +55,7 @@ pub fn target() -> Target {
     options.entry_name = "__main_void".into();
 
     Target {
-        llvm_target: "wasm32-unknown-unknown".into(),
+        llvm_target: "wasm32-wasip2".into(),
         metadata: crate::spec::TargetMetadata {
             description: None,
             tier: None,