[InstCombine] Don't generate crash dialog for fixpoint verification failure (NFC)

Fixpoint verification failures outside our tests are usually not
indicative of a bug -- don't be pushy about having people report them.

Author: nikic

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -5202,7 +5202,8 @@ static bool combineInstructionsOverFunction(
     if (Iteration > Opts.MaxIterations) {
       report_fatal_error(
           "Instruction Combining did not reach a fixpoint after " +
-          Twine(Opts.MaxIterations) + " iterations");
+              Twine(Opts.MaxIterations) + " iterations",
+          /*GenCrashDiag=*/false);
     }
   }