revng2: allow execution in build directory

Change the logic in `python/scripts/revng` to allow executing it as
`revng2`. This allows running `revng2` in the build directory.

python/scripts/revng

@@ -20,6 +20,11 @@ if str(new_path) not in sys.path:
     sys.path.insert(0, str(new_path))
 
 if __name__ == "__main__":
-    from revng.internal.cli.revng import main
+    name = os.path.basename(sys.argv[0])
+    assert name in ("revng", "revng2")
+    if name == "revng":
+        from revng.internal.cli.revng import main
+    else:
+        from revng.internal.cli.revng2 import main
 
     sys.exit(main())