Add ability to force lexed tokens' source_locations.

Add ability to force lexed tokens' source_locations.

Use it to force BUILTINS_LOCATION when declaring builtins instead of creating a <built-in> entry in the line_table which is wrong.

	* c-opts.c (c_finish_options): Force BUILTINS_LOCATION for tokens
	defined in cpp_init_builtins and c_cpp_builtins.

	gcc/fortran/ChangeLog
	* cpp.c (gfc_cpp_init): Force BUILTINS_LOCATION for tokens
	defined in cpp_define_builtins.

	libcpp/ChangeLog
	* init.c (cpp_create_reader): Inititalize forced_token_location_p.
	* internal.h (struct cpp_reader): Add field forced_token_location_p.
	* lex.c (_cpp_lex_direct): Use forced_token_location_p.
	(cpp_force_token_locations): New.
	(cpp_stop_forcing_token_locations): New.

From-SVN: r177973