Force LZ4_FORCE_SW_BITCOUNT for Sparc

This change was proposed for Sparc but it's not clear to me
why it's required.  Proper support exists in the lz4 code to
detect the endianness and the required builtins are available
for gcc.  Still I'm including the patch because it will only
impact Sparc and it may resolve a case which hasn't occured
to me.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: marku89 <mar42@kola.li>
Issue #1700

module/zfs/lz4.c

@@ -238,6 +238,9 @@ lz4_decompress_zfs(void *s_start, void *d_start, size_t s_len,
  * kernel
  */
 #undef	LZ4_FORCE_SW_BITCOUNT
+#if defined(__sparc)
+#define	LZ4_FORCE_SW_BITCOUNT
+#endif
 
 /*
  * Compiler Options