Linux 5.16: Resolve ZSTD_isError symbol collision in Linux kernel

Newer zstd code introduced in the main kernel tree now creates a symbol
collision with ZSTD_isError in our ZSTD code. This change relabels our
implementation with a ZFS-specific symbol name, and undoes some
macro-based micro-optimizations that conflict with the attempt to rename
our internal-use version.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Coleman Kane <ckane@colemankane.org>
Closes #12819

module/zstd/include/zstd_compat_wrapper.h

@@ -406,6 +406,7 @@
 	zfs_ZSTD_insertAndFindFirstIndex_internal
 #define	ZSTD_insertBlock zfs_ZSTD_insertBlock
 #define	ZSTD_invalidateRepCodes zfs_ZSTD_invalidateRepCodes
+#define	ZSTD_isError zfs_ZSTD_isError
 #define	ZSTD_isFrame zfs_ZSTD_isFrame
 #define	ZSTD_ldm_adjustParameters zfs_ZSTD_ldm_adjustParameters
 #define	ZSTD_ldm_blockCompress zfs_ZSTD_ldm_blockCompress

module/zstd/lib/zstd.c

@@ -6340,7 +6340,6 @@ extern "C" {
 
 /* ---- static assert (debug) --- */
 #define ZSTD_STATIC_ASSERT(c) DEBUG_STATIC_ASSERT(c)
-#define ZSTD_isError ERR_isError   /* for inlining */
 #define FSE_isError  ERR_isError
 #define HUF_isError  ERR_isError
 
@@ -7347,7 +7346,6 @@ const char* ZSTD_versionString(void) { return ZSTD_VERSION_STRING; }
 /*-****************************************
 *  ZSTD Error Management
 ******************************************/
-#undef ZSTD_isError   /* defined within zstd_internal.h */
 /*! ZSTD_isError() :
  *  tells if a return value is an error code
  *  symbol is required for external callers */