lalr1.cc: destroy $$ when YYERROR is called.

lalr1.cc: destroy $$ when YYERROR is called.

	* data/lalr1.cc (yyreduce): Compute the resulting state before
	running the user action so that yylhs is a valid symbol.
	(yyerrorlab): Since yylhs is complete (it knows its type), we can
	simply call yy_destroy_ to destroy $$ on YYERROR invocations.
	* tests/c++.at (AT_CHECK_VARIANTS): Test YYERROR with variants.