Merge lld trunk r321017 to contrib/llvm/tools/lld.
Merge llvm, clang, lld, lldb, compiler-rt and libc++ r305145, and updatebuild glue.
Merge llvm, clang, lld and lldb trunk r291476.
Update lld to trunk r290819 and resolve conflicts.
Bring lld (release_39 branch, r279477) to contrib