[compiler] Fix unreachable break

This is causing a warning on newer build configs (crrev.com/c/3117087)

Change-Id: I56afc0e5b0df4b345f8d1b27520b7c35ba31b2df
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3122170Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76509}

src/compiler/backend/code-generator.cc

@@ -848,10 +848,10 @@ CodeGenerator::CodeGenResult CodeGenerator::AssembleInstruction(
     case kFlags_trap: {
 #if V8_ENABLE_WEBASSEMBLY
       AssembleArchTrap(instr, condition);
+      break;
 #else
       UNREACHABLE();
 #endif  // V8_ENABLE_WEBASSEMBLY
-      break;
     }
     case kFlags_none: {
       break;