Merging r195679:
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r195679 | rafael | 2013-11-25 12:15:14 -0800 (Mon, 25 Nov 2013) | 12 lines

Don't use nopl in cpus that don't support it.

Patch by Mikulas Patocka. I added the test. I checked that for cpu names that
gas knows about, it also doesn't generate nopl.

The modified cpus:
i686 - there are i686-class CPUs that don't have nopl: Via c3, Transmeta
        Crusoe, Microsoft VirtualBox - see
        https://bbs.archlinux.org/viewtopic.php?pid=775414
k6, k6-2, k6-3, winchip-c6, winchip2 - these are 586-class CPUs
via c3 c3-2 - see https://bugs.archlinux.org/task/19733 as a proof that
        Via c3 and c3-Nehemiah don't have nopl
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_34@195730 91177308-0d34-0410-b5e6-96231b3b80d8