Makesure the build dir exist even we build the packages manually

pyodide_build/buildall.py

@@ -7,7 +7,7 @@ Build all of the packages in a given directory.
 import argparse
 import json
 from pathlib import Path
-import shutil
+import shutil, os
 
 
 from . import common
@@ -20,6 +20,8 @@ def build_package(pkgname, dependencies, packagesdir, outputdir, args):
     for req in reqs:
         build_package(req, dependencies, packagesdir, outputdir, args)
     buildpkg.build_package(packagesdir / pkgname / 'meta.yaml', args)
+    if not os.path.exists(outputdir):
+        os.mkdir(outputdir)
     shutil.copyfile(
         packagesdir / pkgname / 'build' / (pkgname + '.data'),
         outputdir / (pkgname + '.data'))