This is exactly the same memcpy()-in-hot-path xxHash problem, see
community/xxhash commit log for details.

The bug makes "lz4 -1" or "lz4 -t" twice slower on x86_64 however
"lz4 -9" is barely affected (do not use "lz4 -b" for benchmarking
this change since it does not calculate the checksum).

Other aport changes:
 - use short and fast "make check" (unlike extensive "make test")
   for pre-v7 ARM architectures.