[lld] Add and ignore some flags for ld compat.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@171835 91177308-0d34-0410-b5e6-96231b3b80d8
[ELF] Add R_X86_64_64 relocation.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@171836 91177308-0d34-0410-b5e6-96231b3b80d8