Dub make_TOKEN as a public type interface.

Dub make_TOKEN as a public type interface.

	* data/c++.m4 (b4_symbol_constructor_declare)
	(b4_symbol_constructor_define): New empty stubs.
	(b4_public_types_declare, b4_public_types_define): Use them.
	* data/lalr1.cc (b4_symbol_constructor_declare)
	(b4_symbol_constructor_declare_)
	(b4_symbol_constructor_define_, b4_symbol_constructor_define):
	Move to...
	* data/variant.hh: here.
	Remove the "b4_variant_if" parts, as variant.hh is loaded only if
	needed.
	* data/lalr1.cc: No longer invoke b4_symbol_constructor_define and
	b4_symbol_constructor_declare, as it is now done by
	b4_public_types_define and b4_public_types_declare.