Don't forget exe suffix when bootstrapping

tools/bootstrap.py

 def _build_bootstrap_phase(ph: BootstrapPhase, bts_dir: Path) -> None:
     print(f'Build revision: {ph.ref} [This may take a moment]')
     env = os.environ.copy()
-    env['DDS_BOOTSTRAP_PREV_EXE'] = str(PREBUILT_DIR / 'dds')
+    env['DDS_BOOTSTRAP_PREV_EXE'] = str(PREBUILT_DIR / F'dds{EXE_SUFFIX}')
     _run_quiet(
         [
             sys.executable,

tools/build.py

     if os.name == 'nt':
         tc_fpath = ROOT / 'tools/msvc.dds'
     else:
-        tc_fpath = ROOT / 'gcc-9.dds'
+        tc_fpath = ROOT / 'tools/gcc-9.dds'
 
     self_deps_build(dds_exe, str(tc_fpath), paths.SELF_TEST_REPO_DIR,
                     ROOT / 'remote.dds')