fix Issue 12673 - ICE with static assert and __traits(compiles) with non-existent symbol
Merge pull request #3525 from 9rnsr/fix12673

Issue 12673 - ICE with static assert and __traits(compiles) with non-existent symbol
Add license to visitor header
Merge pull request #3523 from ibuclaw/visitorlicense

Add license to visitor header