use simple-object instead of nm to determine if files contain LTO.

use simple-object instead of nm to determine if files contain LTO.

This replaces the use of nm to search for the LTO common symbol marker
and uses simple object to see if there's a section starting with
".gnu.lto_." or ".gnu.offload_lto_"

2018-12-23  Iain Sandoe  <iain@sandoe.co.uk>

	* collect2.c (maybe_run_lto_and_relink): Don’t say we have a temp file
	unless we actually did some LTO.
	(has_lto_section, is_lto_object_file): New.
	(maybe_lto_object_file): Remove.
	(scan_prog_file): Use is_lto_object_file() instead of scanning the
	output of nm.

From-SVN: r267371