bootstrap: Don't assume a compiletest suite path matches its suite name

Author: Zalathar

src/bootstrap/src/core/build_steps/test.rs

@@ -1581,7 +1581,7 @@ note: if you're sure you want to do this, please open an issue as to why. In the
             cmd.arg("--rust-demangler-path").arg(rust_demangler);
         }
 
-        cmd.arg("--src-base").arg(builder.src.join("tests").join(suite));
+        cmd.arg("--src-base").arg(builder.src.join(suite_path));
         cmd.arg("--build-base").arg(testdir(builder, compiler.host).join(suite));
 
         // When top stage is 0, that means that we're testing an externally provided compiler.