antlr4-runtime

Subtree of antlr4 original repo

The branch cpp-runtime-4.8 was created with commands:

git remote add upstream https://github.com/antlr/antlr4.git
git subtree split -P runtime/Cpp/runtime/src -b cpp-runtime-4.8 4.8
git push origin cpp-runtime-4.8

No other original content is copied since it’s too huge for submodule.