[LoopVectorize] Split out RuntimePointerCheck from LoopVectorizationLegality
[LoopVectorize] Split out RuntimePointerCheck from LoopVectorizationLegality

RuntimePointerCheck will be used through LoopAccessAnalysis in
LoopVectorizationLegality.  Later in the patchset it will become a local class
of LoopAccessAnalysis.

NFC.  This is part of the patchset that splits out the memory dependence logic
from LoopVectorizationLegality into a new class LoopAccessAnalysis.
LoopAccessAnalysis will be used by the new Loop Distribution pass.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@227747 91177308-0d34-0410-b5e6-96231b3b80d8

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