Tweak unconditional-branch.ll passing on any hosts, while investigating x86_64-mingw32.

Sorry for the breakage.

For now, it will fail in two ways:

  1. To fail for targeting x86_64-mingw32.
    <stdin>:131:8: note: possible intended match here
    0x30830a0100000002 3 0 1 0 0 is_stmt

  2. To fail not to find the target x86.
    llc: : error: unable to get target for 'x86_64-unknown-unknown',
      see --version and --triple.