Zstd: Integrate v1.5.7 into the ZFS build system

This commit builds on the previous zstd library update and adds the
necessary ZFS integration and build system changes required to make
zstd 1.5.7 compile and function correctly.

Changes:
- Add zstd_preSplit.c (new in 1.5.7) to all build systems.
- Enable x86_64 assembly in userspace (huf_decompress_amd64.S).
- Disable assembly in kernel for RETHUNK/IBT compatibility.
- Disable intrinsics in kernel for EL10 x86_64-v3 baseline.
- Disable tracing in kernel builds for AArch64 compatibility.
- Fix ZSTD_isError symbol renaming with __asm__ directive.
- Rename abs64 to ZSTD_abs64 (FreeBSD kernel conflict).
- Fix bitstream.h attributes (MEM_STATIC -> FORCE_INLINE_TEMPLATE).
- Remove xxhash.c from BSD build (now header-only).
- Update symbol names in zstd_compat_wrapper.h.
- Ignore checkstyle for zstd-in.c.

Kernel assembly disabled for security mitigation compatibility. User
space retains full performance.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Moch <mail@alexmoch.com>
Closes #18089

module/zstd/lib/common/bitstream.h

@@ -102,8 +102,8 @@ typedef enum { BIT_DStream_unfinished = 0,  /* fully refilled */
     } BIT_DStream_status;  /* result of BIT_reloadDStream() */
 
 MEM_STATIC size_t   BIT_initDStream(BIT_DStream_t* bitD, const void* srcBuffer, size_t srcSize);
-MEM_STATIC BitContainerType BIT_readBits(BIT_DStream_t* bitD, unsigned nbBits);
-MEM_STATIC BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD);
+FORCE_INLINE_TEMPLATE BitContainerType BIT_readBits(BIT_DStream_t* bitD, unsigned nbBits);
+FORCE_INLINE_TEMPLATE BIT_DStream_status BIT_reloadDStream(BIT_DStream_t* bitD);
 MEM_STATIC unsigned BIT_endOfDStream(const BIT_DStream_t* bitD);
 
 

module/zstd/lib/common/zstd_common.c

@@ -33,6 +33,7 @@ const char* ZSTD_versionString(void) { return ZSTD_VERSION_STRING; }
 /*! ZSTD_isError() :
  *  tells if a return value is an error code
  *  symbol is required for external callers */
+unsigned ZSTD_isError(size_t code) __asm__("zfs_ZSTD_isError");
 unsigned ZSTD_isError(size_t code) { return ERR_isError(code); }
 
 /*! ZSTD_getErrorName() :