[clang] [llvm] [mlir] [ErrorHandling] Add reportFatalInternalError + reportFatalUsageError (NFC) (PR #138251)

[Jay Foad via cfe-commits]

jayfoad wrote:

Thanks for doing this. I like it. Definitely an improvement on the status quo. I would be tempted to go further, and replace all uses of `report_fatal_error`.

https://github.com/llvm/llvm-project/pull/138251