collect-utils.c, lto-wrapper + mkoffload: Improve -save-temps filename

collect-utils.c, lto-wrapper + mkoffload: Improve -save-temps filename

gcc/ChangeLog:

	* collect-utils.c (collect_execute, fork_execute): Add at-file suffix
	argument.
	* collect-utils.h (collect_execute, fork_execute): Update prototype.
	* collect2.c (maybe_run_lto_and_relink, do_link, main, do_dsymutil):
	Update calls by passing NULL.
	* config/i386/intelmic-mkoffload.c (compile_for_target,
	generate_host_descr_file, prepare_target_image, main): Likewise.
	* config/gcn/mkoffload.c (compile_native, main): Pass at-file suffix.
	* config/nvptx/mkoffload.c (compile_native, main): Likewise.
	* lto-wrapper.c (compile_offload_image): Likewise.