Log Message:
lld: Sync local patches with merged and pending patches upstream

Cherry-pick upstream patch commit 2a0fcae3d4d1fd85d6ae8378d7c6f12430c0087d
[lld] [ELF] Add '-z nognustack' opt to suppress emitting PT_GNU_STAC dummy \ 
option for an AArch64 erratum.

[LLD] Add NetBSD support as a new flavor of LLD (nb.lld)
https://reviews.llvm.org/D69755

Clang >=clang-9.0.0nb3 is required.