Update backend.py

Author: mayeut

_build_backend/backend.py

@@ -108,6 +108,7 @@ def _bootstrap_build(temp_path: str, config_settings: dict[str, list[str] | str]
         msg = f"Invalid sha256 for {archive_url!r}. Expected {archive_sha256!r}, got {sha256!r}"
         raise ValueError(msg)
 
+    prefix_path = temp_path_ / "cmake-install"
     if os.name == "posix":
         assert archive_name.endswith(".tar.gz")
         tar_filter_kwargs = {"filter": "tar"} if hasattr(tarfile, "tar_filter") else {}
@@ -118,7 +119,6 @@ def _bootstrap_build(temp_path: str, config_settings: dict[str, list[str] | str]
         parallel = max(0, int(parallel_str) if parallel_str.isdigit() else 1) or os.cpu_count() or 1
 
         bootstrap_path = next(temp_path_.glob("cmake-*/bootstrap"))
-        prefix_path = temp_path_ / "cmake-install"
         bootstrap_args = [f"--prefix={prefix_path}", "--no-qt-gui", "--no-debugger", "--parallel={parallel}"]
         previous_cwd = Path().absolute()
         os.chdir(bootstrap_path.parent)