Don't use stage0 compiler for wasm-component-ld

Switch it to using a just-built standard library which enables it to be
cross compiled. Additionally allow it access to `min_specialization`
which `ahash`, a dependency, wants.

src/bootstrap/src/core/build_steps/compile.rs

@@ -1837,7 +1837,7 @@ impl Step for Assemble {
             // `wasm32-wasip2` target of Rust.
             let wasm_component_ld_exe =
                 builder.ensure(crate::core::build_steps::tool::WasmComponentLd {
-                    compiler: build_compiler.with_stage(0),
+                    compiler: build_compiler,
                     target: target_compiler.host,
                 });
             builder.copy_link(

src/bootstrap/src/core/build_steps/tool.rs

@@ -337,7 +337,7 @@ bootstrap_tool!(
     RustdocGUITest, "src/tools/rustdoc-gui-test", "rustdoc-gui-test", is_unstable_tool = true, allow_features = "test";
     CoverageDump, "src/tools/coverage-dump", "coverage-dump";
     RustcPerfWrapper, "src/tools/rustc-perf-wrapper", "rustc-perf-wrapper";
-    WasmComponentLd, "src/tools/wasm-component-ld", "wasm-component-ld";
+    WasmComponentLd, "src/tools/wasm-component-ld", "wasm-component-ld", is_unstable_tool = true, allow_features = "min_specialization";
 );
 
 #[derive(Debug, Clone, Hash, PartialEq, Eq)]