Abort on out of bounds accesses.

Previously out of bounds accesses would trigger undefined behavior.

PiperOrigin-RevId: 851463137

Author: protobuf-github-bot

src/google/protobuf/port.h

@@ -841,7 +841,8 @@ PROTOBUF_EXPORT extern GlobalEmptyString fixed_address_empty_string;
 enum class BoundsCheckMode { kNoEnforcement, kReturnDefault, kAbort };
 
 PROTOBUF_EXPORT constexpr BoundsCheckMode GetBoundsCheckMode() {
-#if defined(PROTOBUF_INTERNAL_BOUNDS_CHECK_MODE_ABORT)
+#if defined(PROTO2_OPENSOURCE) || \
+    defined(PROTOBUF_INTERNAL_BOUNDS_CHECK_MODE_ABORT)
   return BoundsCheckMode::kAbort;
 #elif defined(PROTOBUF_INTERNAL_BOUNDS_CHECK_MODE_RETURN_DEFAULT)
   return BoundsCheckMode::kReturnDefault;