fix an unused function compiler warning in crc32c in 32-bit mode

util/crc32c.cc

@@ -292,10 +292,12 @@ static inline uint32_t LE_LOAD32(const uint8_t *p) {
 }
 
 #ifdef __SSE4_2__
+#ifdef __LP64__
 static inline uint64_t LE_LOAD64(const uint8_t *p) {
   return DecodeFixed64(reinterpret_cast<const char*>(p));
 }
 #endif
+#endif
 
 static inline void Slow_CRC32(uint64_t* l, uint8_t const **p) {
   uint32_t c = static_cast<uint32_t>(*l ^ LE_LOAD32(*p));