ensure that sysroot is properly set for cross-targets

Previously, doing `x test compiler/*` would fail the build due to missing std.
This change ensures that it is prepared.

Signed-off-by: onur-ozkan <work@onurozkan.dev>

Author: onur-ozkan

Diff for: src/bootstrap/src/core/build_steps/test.rs

@@ -2563,8 +2563,17 @@ impl Step for Crate {
         let target = self.target;
         let mode = self.mode;
 
-        // See [field@compile::Std::force_recompile].
-        builder.ensure(compile::Std::force_recompile(compiler, target));
+        // If we're not in stage 0, then we won't have a std from the beta
+        // compiler around. That means we need to make sure there's one in
+        // the sysroot for the compiler to find. Otherwise, we're going to
+        // fail when building crates that need to generate code (e.g., build
+        // scripts and their dependencies).
+        if compiler.stage != 0 {
+            // See [field@compile::Std::force_recompile].
+            builder.ensure(compile::Std::force_recompile(compiler, target));
+            builder.ensure(compile::Std::force_recompile(compiler, compiler.host));
+        }
+
         builder.ensure(RemoteCopyLibs { compiler, target });
 
         // If we're not doing a full bootstrap but we're testing a stage2