Fix corrupted .eh_frame section with LTO and --gc-sections.

Fix corrupted .eh_frame section with LTO and --gc-sections.

Backport from trunk:

When --gc-sections is turned on during an LTO link, the .eh_frame sections
from deferred files are processed before those from the replacement files.
As a result, the section end-cap from crtendS.o is placed ahead of
the .eh_frame data from the replacement files. This patch fixes the bug
by skipping the layout of the deferred sections during GC pass 2.

gold/
	PR gold/17639
	* object.cc (Sized_relobj_file): Initialize is_deferred_layout_.
	(Sized_relobj_file::do_layout): Handle deferred sections properly
	during GC pass 1. Don't add reloc sections to deferred list twice.
	* object.h (Sized_relobj_file::is_deferred_layout): New function.
	(Sized_relobj_file::is_deferred_layout_): New data member.