gold: Properly align the NT_GNU_PROPERTY_TYPE_0 note

The NT_GNU_PROPERTY_TYPE_0 note should be aligned to 8 bytes for 64-bit
ELF as specified by gABI.  A note section can be only placed in a PT_NOTE
segment with the same alignment.

	PR gold/22914
	PR gold/23535
	* layout.cc (Layout::attach_allocated_section_to_segment): Place
	a note section in a PT_NOTE segment with the same alignment.  Set
	the alignment of the PT_NOTE segment from the alignment of the
	note section.
	(Layout::create_note): Align the NT_GNU_PROPERTY_TYPE_0 note to 8
	bytes for 64-bit ELF.
	(Layout::segment_precedes): Place segments with larger alignments
	first.
	* output.cc (Output_segment::Output_segment): Initialize align_.
	* output.h (Output_segment): Add align, set_align and align_.
	* testsuite/Makefile.am (gnu_property_test.stdout): Pass -lhSWn
	to $(TEST_READELF).
	(gnu_property_test): Pass --build-id to ld.
	* testsuite/Makefile.in: Regenerated.
	* testsuite/gnu_property_test.sh (check_alignment): New.
	Use check_alignment to check the NT_GNU_PROPERTY_TYPE_0 note
	alignment.  Verify that there are 2 PT_NOTE segments.