xxhash can be included twice in any order

Previously,

followed by :

would fail to include the static definitions,
because the second include was simply skipped by guard macro.

Now it works as intended :
the missing static part is included during the second include.

lib/common/xxhash.h

@@ -64,16 +64,12 @@ XXH64       13.8 GB/s            1.9 GB/s
 XXH32        6.8 GB/s            6.0 GB/s
 */
 
-#ifndef XXHASH_H_5627135585666179
-#define XXHASH_H_5627135585666179 1
-
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
-#ifndef XXH_NAMESPACE
+#ifndef XXHASH_H_5627135585666179
-#  define XXH_NAMESPACE ZSTD_  /* Zstandard specific */
+#define XXHASH_H_5627135585666179 1
-#endif
 
 
 /* ****************************
@@ -242,6 +238,11 @@ XXH_PUBLIC_API void XXH64_copyState(XXH64_state_t* restrict dst_state, const XXH
 /* **************************
 *  Canonical representation
 ****************************/
+/* Default result type for XXH functions are primitive unsigned 32 and 64 bits.
+*  The canonical representation uses human-readable write convention, aka big-endian (large digits first).
+*  These functions allow transformation of hash result into and from its canonical format.
+*  This way, hash values can be written into a file / memory, and remain comparable on different systems and programs.
+*/
 typedef struct { unsigned char digest[4]; } XXH32_canonical_t;
 typedef struct { unsigned char digest[8]; } XXH64_canonical_t;
 
@@ -251,14 +252,9 @@ XXH_PUBLIC_API void XXH64_canonicalFromHash(XXH64_canonical_t* dst, XXH64_hash_t
 XXH_PUBLIC_API XXH32_hash_t XXH32_hashFromCanonical(const XXH32_canonical_t* src);
 XXH_PUBLIC_API XXH64_hash_t XXH64_hashFromCanonical(const XXH64_canonical_t* src);
 
-/* Default result type for XXH functions are primitive unsigned 32 and 64 bits.
+#endif /* XXHASH_H_5627135585666179 */
-*  The canonical representation uses human-readable write convention, aka big-endian (large digits first).
-*  These functions allow transformation of hash result into and from its canonical format.
-*  This way, hash values can be written into a file / memory, and remain comparable on different systems and programs.
-*/
 
 
-#ifdef XXH_STATIC_LINKING_ONLY
 
 /* ================================================================================================
    This section contains definitions which are not guaranteed to remain stable.
@@ -266,6 +262,8 @@ XXH_PUBLIC_API XXH64_hash_t XXH64_hashFromCanonical(const XXH64_canonical_t* src
    They shall only be used with static linking.
    Never use these definitions in association with dynamic linking !
 =================================================================================================== */
+#if defined(XXH_STATIC_LINKING_ONLY) && !defined(XXH_STATIC_H_3543687687345)
+#define XXH_STATIC_H_3543687687345
 
 /* These definitions are only meant to allow allocation of XXH state
    statically, on stack, or in a struct for example.
@@ -299,11 +297,9 @@ XXH_PUBLIC_API XXH64_hash_t XXH64_hashFromCanonical(const XXH64_canonical_t* src
 #    include "xxhash.c"   /* include xxhash functions as `static`, for inlining */
 #  endif
 
-#endif /* XXH_STATIC_LINKING_ONLY */
+#endif /* XXH_STATIC_LINKING_ONLY && XXH_STATIC_H_3543687687345 */
 
 
 #if defined (__cplusplus)
 }
 #endif
-
-#endif /* XXHASH_H_5627135585666179 */