Use source_location where it is due

libcpp/

	* directives.c (struct if_stack): Use source_location as type
	here.
	* include/cpplib.h (struct cpp_callbacks)<include, define, undef,
	indent, def_pragma, used_define, used_undef>: Properly use
	source_location as parameter type, rather than unsigned int.

From-SVN: r176333