Recent lexer perf compile error with alex-3.5.1.0
Summary
This commit yields a Lexer.hs that doesn't compile when using alex-3.5.1.0 (prevailing version on Hackage). Errors look like
compiler/GHC/Parser/Lexer.x:2871:20: error: [GHC-88464]
Data constructor not in scope: C# :: t0 -> Char
Suggested fixes:
• Perhaps use one of these:
‘GHC.Exts.C#’ (imported from GHC.Exts),
‘GHC.Exts.D#’ (imported from GHC.Exts),
‘GHC.Exts.F#’ (imported from GHC.Exts)
• Perhaps you want to add ‘C#’ to the import list in the import of
‘GHC.Exts’