Pull in r293773 from upstream llvm trunk (by Sanjay Patel):

Pull in r293773 from upstream llvm trunk (by Sanjay Patel):

  [ValueTracking] avoid crashing from bad assumptions (PR31809)

  A program may contain llvm.assume info that disagrees with other
  analysis. This may be caused by UB in the program, so we must not
  crash because of that.

  As noted in the code comments:
  https://llvm.org/bugs/show_bug.cgi?id=31809
  ...we can do better, but this at least avoids the assert/crash in the
  bug report.

  Differential Revision: https://reviews.llvm.org/D29395

This fixes an assertion when building editors/emacs-devel.

PR:		216614