Remove an over zealous assert. The assert was trying to catch places where a chain outside of the loop block-set ended up in the worklist for scheduling as part of the contiguous loop. However, asserting the first block in the chain is in the loop-set isn't a valid check -- we may be forced to drag a chain into the worklist due to one block in the chain being part of the loop even though the first block is *not* in the loop. This occurs when we have been forced to form a chain early due to un-analyzable branches.
Remove an over zealous assert. The assert was trying to catch places
where a chain outside of the loop block-set ended up in the worklist for
scheduling as part of the contiguous loop. However, asserting the first
block in the chain is in the loop-set isn't a valid check -- we may be
forced to drag a chain into the worklist due to one block in the chain
being part of the loop even though the first block is *not* in the loop.
This occurs when we have been forced to form a chain early due to
un-analyzable branches.

No test case here as I have no idea how to even begin reducing one, and
it will be hopelessly fragile. We have to somehow end up with a loop
header of an inner loop which is a successor of a basic block with an
unanalyzable pair of branch instructions. Ow. Self-host triggers it so
it is unlikely it will regress.

This at least gets block placement back to passing selfhost and the test
suite. There are still a lot of slowdown that I don't like coming out of
block placement, although there are now also a lot of speedups. =[ I'm
seeing swings in both directions up to 10%. I'm going to try to find
time to dig into this and see if we can turn this on for 3.1 as it does
a really good job of cleaning up after some loops that degraded with the
inliner changes.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@154287 91177308-0d34-0410-b5e6-96231b3b80d8

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