[compiler] Revert to non-bitfields for Truncation fields.

Reverts part of the change https://chromium-review.googlesource.com/c/v8/v8/+/2892664
to avoid using bitfields for Truncation since it causes older versions of gcc
to report a warning.

BUG=v8:9684

Change-Id: Ia807d6dbbb5ae1baae73bf5816c336b9b80ae83d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2900660
Auto-Submit: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74624}

src/compiler/representation-change.h

@@ -17,10 +17,6 @@ namespace compiler {
 class TypeCache;
 
 enum IdentifyZeros : uint8_t { kIdentifyZeros, kDistinguishZeros };
-constexpr int kIdentifyZerosBits = 1;
-static_assert(static_cast<int>(IdentifyZeros::kDistinguishZeros) <
-                  1 << kIdentifyZerosBits,
-              "kIdentifyZeros must fit into kIdentifyZerosBits");
 
 class Truncation final {
  public:
@@ -98,10 +94,6 @@ class Truncation final {
     kOddballAndBigIntToNumber,
     kAny
   };
-  static constexpr int kTruncationKindBits = 4;
-  static_assert(static_cast<int>(TruncationKind::kAny) <
-                    1 << kTruncationKindBits,
-                "TransactionKind must fit into kTruncationKindBits");
 
   explicit Truncation(TruncationKind kind, IdentifyZeros identify_zeros)
       : kind_(kind), identify_zeros_(identify_zeros) {
@@ -111,8 +103,8 @@ class Truncation final {
   }
   TruncationKind kind() const { return kind_; }
 
-  TruncationKind kind_ : kTruncationKindBits;
-  IdentifyZeros identify_zeros_ : kIdentifyZerosBits;
+  TruncationKind kind_;
+  IdentifyZeros identify_zeros_;
 
   static TruncationKind Generalize(TruncationKind rep1, TruncationKind rep2);
   static IdentifyZeros GeneralizeIdentifyZeros(IdentifyZeros i1,