The current CVS version of pl/plpgsql/src/gram.y may work for plain
yacc, but it fails with bison :-(
I think the only real solution will be to stop trying to compile the
yacc and lex output files as one C compilation, and compile them
separately like everyone else does it...
In the meantime I suggest reverting the "fix", since most of the
developers are presumably using bison.
regards, tom lane