Fuse the three stacks into a single one.

Fuse the three stacks into a single one.

In order to make it easy to perform benchmarks to ensure that there are no
performance loss, lalr1.cc is forked into lalr1-fusion.cc.  Eventually,
lalr1-fusion.cc will replace lalr1.cc.

Meanwhile, to make sure that lalr1-fusion.cc is correctly exercized by the
test suite, the user must install a symbolic link from lalr1.cc to it.

Instead of having three stacks (state, value, location), use a stack
of triples.  This considerably simplifies the code (and it will be
easier not to require locations as currently does the C++ parser),
and also gives a 10% speedup according to etc/bench (probably mainly since
memory allocation is done once instead of three times).

Another motivation is to make it easier to destruct properly
semantic values: now that they are bound to their state (hence
symbol type) it will be easier to call the appropriate destructor.

These changes should probably benefit the C parser too.

	* data/lalr1.cc: Copy as...  * data/lalr1-fusion.cc: this new
	file.
	(b4_rhs_value, b4_rhs_location): New definitions overriding those
	from c++.m4.
	(state_stack_type, semantic_stack_type, location_stack_type)
	(yystate_stack_, yysemantic_stack_, yylocation_stack_): Remove.
	(data_type, stack_type, yystack_): New.
	(YYLLOC_DEFAULT, yypush_): Adjust.
	(yyerror_range): Now based on data_type, not location_type.