revamp intelmic-mkoffload aux dump names

revamp intelmic-mkoffload aux dump names

Rework intelmic-mkoffload into the new aux and dump file naming
semantics.  Obey -save-temps.

Co-Authored-By: Thomas Schwinge <thomas@codesourcery.com>
for  gcc/ChangeLog

	* config/i386/intelmic-mkoffload.c
	(generate_target_descr_file): Use dumppfx for save_temps
	files.  Pass -dumpbase et al down to the compiler.
	(generate_target_offloadend_file): Likewise.
	(generate_host_descr_file): Likewise.
	(prepare_target_image): Likewise.  Move out_obj_filename
	setting...
	(main): ... here.  Detect -dumpbase, set dumppfx too.