The .note.gnu.property SHT_NOTE sections on AArch64 (a 64-bit target) should have alignment 8 to more closely match the binutils implementation where alignment is 4-bytes on 32-bit machines and 8-bytes on 64-bit machines.
Previously LLD was using 4 for both 32-bit and 64-bit machines.
There was a long discussion on the right alignment of the .note.gnu.property section on the binutils mailing list. The basic argument was that generic ELF requires 8-byte alignment for SHT_NOTES sections, however this hadn't been respected by other GNU notes sections. The implementation in GNU ld uses 8 and as there is no binary legacy of using 4 in LLD (BTI is only just being picked up and used) I'd like to keep LLD in line with GNU ld.
Although at present LLD only does something useful with AArch64 properties, this also applies to X86.
Depends on D70961 as it updates a test added there.