Fix exporting of (->) instances. This is the fix from the web page
with minor changes for the new continuation-passing lexer.
','# -> lex_tuple cont module_dot (stepOnBy# buf 2#)
_ -> lex_id3 cont module_dot buf
':'# -> lex_id3 cont module_dot (incLexeme buf)
+ '-'# ->
+ case module_dot of
+ Nothing -> lex_id3 cont module_dot buf
+ Just ghc -> -- this should be "GHC" (current home of (->))
+ case lookAhead# buf 1# of
+ '>'# -> end_lex_id cont module_dot (ITconid SLIT("->"))
+ (stepOnBy# buf 2#)
+ _ -> lex_id3 cont module_dot buf
_ -> lex_id3 cont module_dot buf