ld: Add -plugin-save-temps

ld: Add -plugin-save-temps

Add -plugin-save-temps to store plugin intermediate files permanently.
It can be used to exam the final input object files generated from IR
inputs.

	* NEWS: Mention -plugin-save-temps.
	* ld.h (ld_config_type): Add plugin_save_temps.
	* ld.texi: Document -plugin-save-temps.
	* ldlex.h (option_values): Add OPTION_PLUGIN_SAVE_TEMPS.
	* lexsup.c (ld_options): Add -plugin-save-temps.
	(parse_args): Handle OPTION_PLUGIN_SAVE_TEMPS.
	* plugin.c (plugin_call_cleanup): Don't call plugin
	cleanup_handler for -plugin-save-temps.