Fix inconsistent "defined()" operator usage which causes compile warnings if undefined.
#include <ngtcp2/ngtcp2.h>
-#if defined HAVE_BSWAP_64 || HAVE_DECL_BSWAP_64
+#if defined(HAVE_BSWAP_64) || (defined(HAVE_DECL_BSWAP_64) && HAVE_DECL_BSWAP_64 > 0)
# define ngtcp2_bswap64 bswap_64
#else /* !HAVE_BSWAP_64 */
# define ngtcp2_bswap64(N) \
((uint64_t)(ntohl((uint32_t)(N))) << 32 | ntohl((uint32_t)((N) >> 32)))
#endif /* !HAVE_BSWAP_64 */
-#if defined HAVE_BE64TOH || HAVE_DECL_BE64TOH
+#if defined(HAVE_BE64TOH) || (defined(HAVE_DECL_BE64TOH) && HAVE_DECL_BE64TOH > 0)
# define ngtcp2_ntohl64(N) be64toh(N)
# define ngtcp2_htonl64(N) htobe64(N)
#else /* !HAVE_BE64TOH */
-# if defined WORDS_BIGENDIAN
+# if defined(WORDS_BIGENDIAN)
# define ngtcp2_ntohl64(N) (N)
# define ngtcp2_htonl64(N) (N)
# else /* !WORDS_BIGENDIAN */
