CLEANUP: Move XXH3 macro from haproxy/compat.h to haproxy/xxhash.h

This moves all the xxhash functionality into a single location.

see d5fc8fcb86eb99831626051b3055bea7ca93a074
diff --git a/include/haproxy/compat.h b/include/haproxy/compat.h
index 72dc3dc..886b7a3 100644
--- a/include/haproxy/compat.h
+++ b/include/haproxy/compat.h
@@ -288,13 +288,6 @@
  */
 #define MAX_SEND_FD 253
 
-/* Make the new complex name for the xxhash function easier to remember
- * and use.
- */
-#ifndef XXH3
-#define XXH3(data, len, seed) XXH3_64bits_withSeed(data, len, seed)
-#endif
-
 #endif /* _HAPROXY_COMPAT_H */
 
 /*
diff --git a/include/haproxy/xxhash.h b/include/haproxy/xxhash.h
index 83a2fb7..cd333e6 100644
--- a/include/haproxy/xxhash.h
+++ b/include/haproxy/xxhash.h
@@ -42,4 +42,11 @@
 
 #include <import/xxhash.h>
 
+/* Make the new complex name for the xxhash function easier to remember
+ * and use.
+ */
+#ifndef XXH3
+#define XXH3(data, len, seed) XXH3_64bits_withSeed(data, len, seed)
+#endif
+
 #endif