S390 [simd]: mark load/store lane as unreachable

Change-Id: Ifdfdddb0b36cfefc25ba11d8884b30fcda04a494
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3032264Reviewed-by: Junliang Yan <junyan@redhat.com>
Commit-Queue: Milad Fa <mfarazma@redhat.com>
Cr-Commit-Position: refs/heads/master@{#75760}

src/compiler/backend/s390/instruction-selector-s390.cc

@@ -2790,7 +2790,7 @@ void InstructionSelector::EmitPrepareResults(
 
 void InstructionSelector::VisitLoadLane(Node* node) {
   // We should never reach here, see http://crrev.com/c/2577820
-  UNIMPLEMENTED();
+  UNREACHABLE();
 }
 
 void InstructionSelector::VisitLoadTransform(Node* node) {
@@ -2800,7 +2800,7 @@ void InstructionSelector::VisitLoadTransform(Node* node) {
 
 void InstructionSelector::VisitStoreLane(Node* node) {
   // We should never reach here, see http://crrev.com/c/2577820
-  UNIMPLEMENTED();
+  UNREACHABLE();
 }
 
 void InstructionSelector::VisitTruncateFloat32ToInt32(Node* node) {