[ELF] Add missing -target options.

These tests assume that the created objects are for x86_64. These tests
failed on non-x86_64 environments, such as 32 bit Windows.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@193910 91177308-0d34-0410-b5e6-96231b3b80d8