[SCEV] Limit recursion depth of constant evolving.
[SCEV] Limit recursion depth of constant evolving.

- For a loop body with VERY complicated exit condition evaluation, constant
  evolving may run out of stack on platforms such as Windows. Need to limit the
  recursion depth.

Differential Revision: https://reviews.llvm.org/D28629



git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@291927 91177308-0d34-0410-b5e6-96231b3b80d8

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