[llvm] [TableGen] Use PrintFatalError in ParseTreePattern for proper error handling of llvm-tblgen (PR #161417)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

Missing new test. The only test changes appear to be regressing error quality in covered cases. In general non-fatal errors are preferable. It's better to emit as many errors as possible 

https://github.com/llvm/llvm-project/pull/161417