Pull in r322016 from upstream llvm trunk (by Sanjay Patel):

[ValueTracking] remove overzealous assert

  The test is derived from a failing fuzz test:
  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=5008

  Credit to @rksimon for pointing out the problem.

This should fix "Bad flavor while matching min/max" errors when building
the graphics/libsixel and science/kst2 ports.

Reported by:	jbeich
PR:		225268, 225269

contrib/llvm/lib/Analysis/ValueTracking.cpp

@@ -4214,7 +4214,7 @@ static SelectPatternResult matchMinMaxOfMinMax(CmpInst::Predicate Pred,
       break;
     return {SPF_UNKNOWN, SPNB_NA, false};
   default:
-    llvm_unreachable("Bad flavor while matching min/max");
+    return {SPF_UNKNOWN, SPNB_NA, false};
   }
 
   // a pred c ? m(a, b) : m(c, b) --> m(m(a, b), m(c, b))