fix: ha_seed_jitter loop-until-full partial read; byteorder.h musl portability

src/include/byteorder.h

@@ -1,7 +1,24 @@
 #pragma once
-/* Portable be64toh() for non-glibc or pre-2.25 targets. */
+/* Portable be64toh() — big-endian to host byte order conversion. */
 #if defined(__linux__)
+#  ifndef _DEFAULT_SOURCE
+#    define _DEFAULT_SOURCE 1
+#  endif
+#  ifndef _BSD_SOURCE
+#    define _BSD_SOURCE 1
+#  endif
 #  include <endian.h>
+#  ifndef be64toh
+   /* musl and some older glibc: fall back to builtin */
+#  include <stdint.h>
+static inline uint64_t be64toh(uint64_t x) {
+#    if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+    return __builtin_bswap64(x);
+#    else
+    return x;
+#    endif
+}
+#  endif /* be64toh */
 #elif defined(__APPLE__)
 #  include <machine/endian.h>
 #  include <libkern/OSByteOrder.h>