Unbuffered mode for bootstrap build scripts

tools/bootstrap.py

 BOOTSTRAP_DIR = BUILD_DIR / '_bootstrap'
 PREBUILT_DIR = PROJECT_ROOT / '_prebuilt'
 
+EXE_SUFFIX = '.exe' if os.name == 'nt' else ''
+
 
 def _run_quiet(args) -> None:
     cmd = [str(s) for s in args]
 def _build_bootstrap_phase(ph: str, args: argparse.Namespace) -> None:
     print(f'Running build: {ph} (Please wait a moment...)')
     env = os.environ.copy()
-    env['DDS_BOOTSTRAP_PREV_EXE'] = PREBUILT_DIR / 'dds'
+    env['DDS_BOOTSTRAP_PREV_EXE'] = str(PREBUILT_DIR / 'dds')
     subprocess.check_call(
         [
             sys.executable,
+            '-u',
             str(BOOTSTRAP_DIR / 'tools/build.py'),
             f'--cxx={args.cxx}',
         ],
 def _pull_executable() -> Path:
     prebuild_dir = (PROJECT_ROOT / '_prebuilt')
     prebuild_dir.mkdir(exist_ok=True)
-    exe, = list(BOOTSTRAP_DIR.glob('_build/dds*'))
+    generated = list(BOOTSTRAP_DIR.glob(f'_build/dds{EXE_SUFFIX}'))
+    assert len(generated) == 1, repr(generated)
+    exe, = generated
     dest = prebuild_dir / exe.name
     exe.rename(dest)
     return dest