lalr1.cc: don't generate location.hh when location_type is defined

lalr1.cc: don't generate location.hh when location_type is defined

	* data/bison.m4 (b4_percent_define_get): Accept a default value.
	* data/c++.m4: Do not provide a default value for the %define
	variable location_type, rather, use b4_percent_define_get with a
	default argument where its value is needed.
	* data/lalr1.cc: Do not load location.cc (which outputs both
	location.hh and position.hh) if the user defined location_type.
	Do not include location.hh either.