Fix compiler warnings about unused variables in wire_format.h

src/google/protobuf/wire_format.h

diff --git a/src/google/protobuf/wire_format.h b/src/google/protobuf/wire_format.h
index de8ea57..5e9aca5 100644
--- a/src/google/protobuf/wire_format.h
+++ b/src/google/protobuf/wire_format.h
@@ -327,6 +327,9 @@
 #ifdef GOOGLE_PROTOBUF_UTF8_VALIDATION_ENABLED
   WireFormatLite::VerifyUtf8String(
       data, size, static_cast<WireFormatLite::Operation>(op), field_name);
+#else
+  // Avoid the compiler warning about unused variables.
+  (void)data; (void)size; (void)op; (void)field_name;
 #endif
 }