zstd: Update to upstream version 1.3.1

It is now dual-licensed BSD-3-Clause and GPL-2.0, we use the former.
The PATENTS file is no longer applicable \o/

Also add zstd to COPYRIGHT.txt

thirdparty/zstd/common/fse.h

@@ -31,13 +31,14 @@
    You can contact the author at :
    - Source repository : https://github.com/Cyan4973/FiniteStateEntropy
 ****************************************************************** */
-#ifndef FSE_H
-#define FSE_H
 
 #if defined (__cplusplus)
 extern "C" {
 #endif
 
+#ifndef FSE_H
+#define FSE_H
+
 
 /*-*****************************************
 *  Dependencies
@@ -297,8 +298,10 @@ FSE_decompress_usingDTable() result will tell how many bytes were regenerated (<
 If there is an error, the function will return an error code, which can be tested using FSE_isError(). (ex: dst buffer too small)
 */
 
+#endif  /* FSE_H */
 
-#ifdef FSE_STATIC_LINKING_ONLY
+#if defined(FSE_STATIC_LINKING_ONLY) && !defined(FSE_H_FSE_STATIC_LINKING_ONLY)
+#define FSE_H_FSE_STATIC_LINKING_ONLY
 
 /* *** Dependency *** */
 #include "bitstream.h"
@@ -381,6 +384,11 @@ size_t FSE_buildDTable_rle (FSE_DTable* dt, unsigned char symbolValue);
 size_t FSE_decompress_wksp(void* dst, size_t dstCapacity, const void* cSrc, size_t cSrcSize, FSE_DTable* workSpace, unsigned maxLog);
 /**< same as FSE_decompress(), using an externally allocated `workSpace` produced with `FSE_DTABLE_SIZE_U32(maxLog)` */
 
+typedef enum {
+   FSE_repeat_none,  /**< Cannot use the previous table */
+   FSE_repeat_check, /**< Can use the previous table but it must be checked */
+   FSE_repeat_valid  /**< Can use the previous table and it is asumed to be valid */
+ } FSE_repeat;
 
 /* *****************************************
 *  FSE symbol compression API
@@ -694,5 +702,3 @@ MEM_STATIC unsigned FSE_endOfDState(const FSE_DState_t* DStatePtr)
 #if defined (__cplusplus)
 }
 #endif
-
-#endif  /* FSE_H */