--- sys/contrib/zstd/lib/freebsd/zstd_kfreebsd.h        (revision 327712)
+++ sys/contrib/zstd/lib/freebsd/zstd_kfreebsd.h        (working copy)
@@ -49,6 +49,44 @@
 #define calloc(a,b)    (malloc)((a)*(b), M_ZSTD, M_WAITOK | M_ZERO)
 #endif

+#undef __builtin_ctz
+#undef __builtin_ctzll
+#undef __builtin_clz
+#undef __builtin_clzll
+#undef __builtin_bswap32
+#undef __builtin_bswap64
+
+#define __builtin_bswap32 bswap32
+#define __builtin_bswap64 bswap64
+
+static inline int
+__builtin_ctz(int x)
+{
+       if (x == 0)
+               return (sizeof(x) * NBBY);
+       return (ffs(x) - 1);
+}
+
+static inline long long
+__builtin_ctzll(long long x)
+{
+       if (x == 0)
+               return (sizeof(x) * NBBY);
+       return (ffsll(x) - 1);
+}
+
+static inline int
+__builtin_clz(int x)
+{
+       return (sizeof(x) * NBBY - fls(x));
+}
+
+static inline long long
+__builtin_clzll(long long x)
+{
+       return (sizeof(x) * NBBY - flsll(x));
+}
+
 #ifdef __cplusplus
 }
 #endif