* cp-tree.h (class iloc_sentinel): New.

We didn't already have a sentinel for input_location, and while
temp_override would work, it would also happily set input_location to 0,
which breaks things that try to look up the associated filename.

	* decl.c (grokdeclarator, finish_enum_value_list): Use it.
	* mangle.c (mangle_decl_string): Use it.
	* pt.c (perform_typedefs_access_check): Use it.

From-SVN: r276191