Add pyodide_build/__main__.py

pyodide_build/__main__.py

+#!/usr/bin/env python3
+import argparse
+
+from . import buildall
+from . import buildpkg
+from . import pywasmcross
+
+
+def main():
+    main_parser = argparse.ArgumentParser()
+    subparsers = main_parser.add_subparsers(help='action')
+
+    for command_name, module in (("buildpkg", buildpkg),
+                                 ("buildall", buildall),
+                                 ("pywasmcross", pywasmcross)):
+        parser = module.make_parser(subparsers.add_parser(command_name))
+        parser.set_defaults(func=module.main)
+
+    args = main_parser.parse_args()
+    # run the selected action
+    args.func(args)
+
+
+if __name__ == '__main__':
+    main()