Upgrade versions of vendored libs

vendor/github.com/DataDog/zstd/threading.h

@@ -17,10 +17,6 @@
 
 #include "debug.h"
 
-#if defined (__cplusplus)
-extern "C" {
-#endif
-
 #if defined(ZSTD_MULTITHREAD) && defined(_WIN32)
 
 /**
@@ -73,7 +69,6 @@ int ZSTD_pthread_join(ZSTD_pthread_t thread);
  * add here more wrappers as required
  */
 
-
 #elif defined(ZSTD_MULTITHREAD)    /* posix assumed ; need a better detection method */
 /* ===   POSIX Systems   === */
 #  include <pthread.h>
@@ -144,9 +139,6 @@ typedef int ZSTD_pthread_cond_t;
 
 #endif /* ZSTD_MULTITHREAD */
 
-#if defined (__cplusplus)
-}
-#endif
 
 #endif /* THREADING_H_938743 */