[wasm] --liftoff-only should disable --wasm-dynamic-tiering

A Liftoff only configuration should never tier up to TurboFan, hence add
a proper implication to disable dynamic tiering if --liftoff-only is
set.
Also, add a DCHECK to ensure we never accidentally compile with TurboFan
if --liftoff-only is set.

R=jkummerow@chromium.org

Bug: v8:12281
Change-Id: Ia9b81add503cc939f59fde3f4d3bb67252facf2c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3569741Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79779}

src/compiler/wasm-compiler.cc

@@ -8440,6 +8440,10 @@ wasm::WasmCompilationResult ExecuteTurbofanWasmCompilation(
     wasm::CompilationEnv* env, const wasm::WireBytesStorage* wire_byte_storage,
     const wasm::FunctionBody& func_body, int func_index, Counters* counters,
     wasm::WasmFeatures* detected) {
+  // Check that we do not accidentally compile a Wasm function to TurboFan if
+  // --liftoff-only is set.
+  DCHECK(!FLAG_liftoff_only);
+
   TRACE_EVENT2(TRACE_DISABLED_BY_DEFAULT("v8.wasm.detailed"),
                "wasm.CompileTopTier", "func_index", func_index, "body_size",
                func_body.end - func_body.start);

src/flags/flag-definitions.h

@@ -1011,6 +1011,7 @@ DEFINE_BOOL(liftoff_only, false,
             "disallow TurboFan compilation for WebAssembly (for testing)")
 DEFINE_IMPLICATION(liftoff_only, liftoff)
 DEFINE_NEG_IMPLICATION(liftoff_only, wasm_tier_up)
+DEFINE_NEG_IMPLICATION(liftoff_only, wasm_dynamic_tiering)
 DEFINE_NEG_IMPLICATION(fuzzing, liftoff_only)
 DEFINE_DEBUG_BOOL(
     enable_testing_opcode_in_wasm, false,