Bug#812852: Vigra auf ppc64el -- continues a little bit

[Ullrich Koethe]

I upgraded the RC to use the newest LZ4 version which has significantly 
better byte order handling. Hopefully, this fixes the problem. One could 
also add a cmake option to use a pre-installed LZ4 library when 
available and just fall-back to the internal version if not.

Best
Ulli