[tools] Add TODO comment to prepare-build-dir

tools/prepare-build-dir

@@ -65,6 +65,9 @@ fi
 
 # Now filter the environment variables for the configuration
 # arguments.
+# TODO: Ideally this should be determined by parsing the meson project
+# name. But this is not easily possibly right now. See
+# https://github.com/mesonbuild/meson/issues/3535
 readonly VARIABLE_PREFIX="EMPER_"
 MESON_ARGS=()
 for var in $(compgen -e); do