[Dev] Update vendored ZSTD to v1.5.6 (duckdb#14360)

This PR was sparked by work on new compression related functionality,
which made me notice that `ZDICT_trainFromBuffer_fastCover` was missing.

In an attempt to add the definition for that function, I was already
bringing in 6+ new files, so I figured I would spin it off in a new PR
that updates the entire ZSTD library we vendor to 1.5.6 (and adds the
missing function definitions + files)

third_party/zstd/CMakeLists.txt

@@ -0,0 +1,52 @@
+if(POLICY CMP0063)
+    cmake_policy(SET CMP0063 NEW)
+endif()
+
+set(ZSTD_FILES
+	compress/zstd_compress_superblock.cpp
+	compress/zstdmt_compress.cpp
+	compress/zstd_double_fast.cpp
+	compress/zstd_fast.cpp
+	compress/zstd_compress_sequences.cpp
+	compress/zstd_ldm.cpp
+	compress/hist.cpp
+	compress/zstd_compress.cpp
+	compress/zstd_lazy.cpp
+	compress/zstd_compress_literals.cpp
+	compress/huf_compress.cpp
+	compress/zstd_opt.cpp
+	compress/fse_compress.cpp
+	decompress/zstd_ddict.cpp
+	decompress/huf_decompress.cpp
+	decompress/zstd_decompress.cpp
+	decompress/zstd_decompress_block.cpp
+	common/entropy_common.cpp
+	common/fse_decompress.cpp
+	common/debug.cpp
+	common/xxhash.cpp
+	common/pool.cpp
+	common/threading.cpp
+	common/zstd_common.cpp
+	common/error_private.cpp
+	dict/cover.cpp
+	dict/divsufsort.cpp
+	dict/fastcover.cpp
+	dict/zdict.cpp
+	deprecated/zbuff_common.cpp
+	deprecated/zbuff_decompress.cpp
+	deprecated/zbuff_compress.cpp
+)
+
+add_library(duckdb_zstd STATIC ${ZSTD_FILES})
+
+target_include_directories(
+  duckdb_zstd
+  PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>)
+set_target_properties(duckdb_zstd PROPERTIES EXPORT_NAME duckdb_duckdb_zstd)
+
+install(TARGETS duckdb_zstd
+        EXPORT "${DUCKDB_EXPORT_SET}"
+        LIBRARY DESTINATION "${INSTALL_LIB_DIR}"
+        ARCHIVE DESTINATION "${INSTALL_LIB_DIR}")
+
+disable_target_warnings(duckdb_zstd)

third_party/zstd/common/debug.cpp

@@ -0,0 +1,36 @@
+/* ******************************************************************
+ * debug
+ * Part of FSE library
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * You can contact the author at :
+ * - Source repository : https://github.com/Cyan4973/FiniteStateEntropy
+ *
+ * This source code is licensed under both the BSD-style license (found in the
+ * LICENSE file in the root directory of this source tree) and the GPLv2 (found
+ * in the COPYING file in the root directory of this source tree).
+ * You may select, at your option, one of the above-listed licenses.
+****************************************************************** */
+
+
+/*
+ * This module only hosts one global variable
+ * which can be used to dynamically influence the verbosity of traces,
+ * such as DEBUGLOG and RAWLOG
+ */
+
+#include "zstd/common/debug.h"
+
+#if !defined(ZSTD_LINUX_KERNEL) || (DEBUGLEVEL>=2)
+
+namespace duckdb_zstd {
+
+/* We only use this when DEBUGLEVEL>=2, but we get -Werror=pedantic errors if a
+ * translation unit is empty. So remove this from Linux kernel builds, but
+ * otherwise just leave it in.
+ */
+int g_debuglevel = DEBUGLEVEL;
+
+} // namespace duckdb_zstd
+
+#endif