Pull in r337861 from upstream llvm trunk (by Hideki Saito):

Pull in r337861 from upstream llvm trunk (by Hideki Saito):

  [LV] Fix for PR38110, LV encountered llvm_unreachable()

  Summary: truncateToMinimalBitWidths() doesn't handle all Instructions
  and the worst case is compiler crash via llvm_unreachable(). Fix is
  to add a case to handle PHINode and changed the worst case to NO-OP
  (from compiler crash).

  Reviewers: sbaranga, mssimpso, hsaito

  Reviewed By: hsaito

  Subscribers: llvm-commits

  Differential Revision: https://reviews.llvm.org/D49461

This should fix "Unhandled instruction type!" (if assertions are
enabled) or segmentation faults (if assertions are disabled) when
compiling certain versions of the net-p2p/gtk-gnutella port.

Direct commit to stable/11 and stable/12, since head already has this
fix.

Reported by:	Jamie Landeg-Jones <jamie@catflap.org>
PR:		234987