Fix definitions of constants for RngSupport

At a low-enough optimization level, even integral constants can end up
odr-used; that causes a link-time failure, if they don't have a definition.

PiperOrigin-RevId: 280737529
Change-Id: I55dd79d86fd83abf9a0bd285081081dfd3e2b128

tensorflow/stream_executor/rng.cc

@@ -40,10 +40,8 @@ bool RngSupport::CheckSeed(const uint8 *seed, uint64 seed_bytes) {
   return true;
 }
 
-#if defined(__APPLE__) || defined(__FreeBSD__)
 const int RngSupport::kMinSeedBytes;
 const int RngSupport::kMaxSeedBytes;
-#endif
 
 }  // namespace rng
 }  // namespace stream_executor