licenses/ANTLR is not a real license, but simply says that the work is in the public domain. If there are no objections, I'll update the ebuilds in a few days from now.
I agree with you. However, the last paragraph makes it a little bit different to other "this code is in public domain" statements.
The last paragraph is only informational. It doesn't change any legal rights. Also we currently don't distinguish between different types of public-domain (like e.g. works released into the public domain by their author, or U.S. government works). Therefore I think that LICENSE="public-domain" is appropriate for ANTLR.
Then feel free to change the license.
Fixed.