[heap] Do not use V8_LIKELY on FLAG_disable_write_barriers.

FLAG_disable_write_barriers is a constexpr so the V8_LIKELY macro isn't
necessary. Interestingly, it can also cause clang to warn that the code
is unreachable, whereas without `__builtin_expect()` the compiler
doesn't mind. See for example:

```
constexpr bool kNo = false;

void warns() {
  if (__builtin_expect(kNo, 0)) {
    int a = 42;
  }
}

void does_not_warn() {
  if (kNo) {
    int a = 42;
  }
}
```

Compiling V8 for arm64 with both `v8_disable_write_barriers = true` and
`v8_enable_pointer_compression = false` would trigger this warning.

Bug: v8:9533
Change-Id: Id2ae156d60217007bb9ebf50628e8908e0193d05
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2534811Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Pierre Langlois <pierre.langlois@arm.com>
Cr-Commit-Position: refs/heads/master@{#71157}

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

@@ -620,8 +620,7 @@ void InstructionSelector::VisitStore(Node* node) {
     write_barrier_kind = kFullWriteBarrier;
   }
 
-  if (write_barrier_kind != kNoWriteBarrier &&
-      V8_LIKELY(!FLAG_disable_write_barriers)) {
+  if (write_barrier_kind != kNoWriteBarrier && !FLAG_disable_write_barriers) {
     DCHECK(CanBeTaggedPointer(rep));
     AddressingMode addressing_mode;
     InstructionOperand inputs[3];

src/compiler/backend/arm64/instruction-selector-arm64.cc

@@ -791,8 +791,7 @@ void InstructionSelector::VisitStore(Node* node) {
   }
 
   // TODO(arm64): I guess this could be done in a better way.
-  if (write_barrier_kind != kNoWriteBarrier &&
-      V8_LIKELY(!FLAG_disable_write_barriers)) {
+  if (write_barrier_kind != kNoWriteBarrier && !FLAG_disable_write_barriers) {
     DCHECK(CanBeTaggedOrCompressedPointer(rep));
     AddressingMode addressing_mode;
     InstructionOperand inputs[3];

src/compiler/backend/ia32/instruction-selector-ia32.cc

@@ -493,8 +493,7 @@ void InstructionSelector::VisitStore(Node* node) {
     write_barrier_kind = kFullWriteBarrier;
   }
 
-  if (write_barrier_kind != kNoWriteBarrier &&
-      V8_LIKELY(!FLAG_disable_write_barriers)) {
+  if (write_barrier_kind != kNoWriteBarrier && !FLAG_disable_write_barriers) {
     DCHECK(CanBeTaggedPointer(rep));
     AddressingMode addressing_mode;
     InstructionOperand inputs[] = {

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

@@ -415,8 +415,7 @@ void InstructionSelector::VisitStore(Node* node) {
   }
 
   // TODO(mips): I guess this could be done in a better way.
-  if (write_barrier_kind != kNoWriteBarrier &&
-      V8_LIKELY(!FLAG_disable_write_barriers)) {
+  if (write_barrier_kind != kNoWriteBarrier && !FLAG_disable_write_barriers) {
     DCHECK(CanBeTaggedPointer(rep));
     InstructionOperand inputs[3];
     size_t input_count = 0;

src/compiler/backend/mips64/instruction-selector-mips64.cc

@@ -494,8 +494,7 @@ void InstructionSelector::VisitStore(Node* node) {
   }
 
   // TODO(mips): I guess this could be done in a better way.
-  if (write_barrier_kind != kNoWriteBarrier &&
-      V8_LIKELY(!FLAG_disable_write_barriers)) {
+  if (write_barrier_kind != kNoWriteBarrier && !FLAG_disable_write_barriers) {
     DCHECK(CanBeTaggedPointer(rep));
     InstructionOperand inputs[3];
     size_t input_count = 0;

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

@@ -283,8 +283,7 @@ void InstructionSelector::VisitStore(Node* node) {
     write_barrier_kind = kFullWriteBarrier;
   }
 
-  if (write_barrier_kind != kNoWriteBarrier &&
-      V8_LIKELY(!FLAG_disable_write_barriers)) {
+  if (write_barrier_kind != kNoWriteBarrier && !FLAG_disable_write_barriers) {
     DCHECK(CanBeTaggedOrCompressedPointer(rep));
     AddressingMode addressing_mode;
     InstructionOperand inputs[3];

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

@@ -721,8 +721,7 @@ static void VisitGeneralStore(
   Node* base = node->InputAt(0);
   Node* offset = node->InputAt(1);
   Node* value = node->InputAt(2);
-  if (write_barrier_kind != kNoWriteBarrier &&
-      V8_LIKELY(!FLAG_disable_write_barriers)) {
+  if (write_barrier_kind != kNoWriteBarrier && !FLAG_disable_write_barriers) {
     DCHECK(CanBeTaggedOrCompressedPointer(rep));
     AddressingMode addressing_mode;
     InstructionOperand inputs[3];

src/compiler/backend/x64/instruction-selector-x64.cc

@@ -479,8 +479,7 @@ void InstructionSelector::VisitStore(Node* node) {
     write_barrier_kind = kFullWriteBarrier;
   }
 
-  if (write_barrier_kind != kNoWriteBarrier &&
-      V8_LIKELY(!FLAG_disable_write_barriers)) {
+  if (write_barrier_kind != kNoWriteBarrier && !FLAG_disable_write_barriers) {
     DCHECK(CanBeTaggedOrCompressedPointer(store_rep.representation()));
     AddressingMode addressing_mode;
     InstructionOperand inputs[] = {