Shrink.cc does not work on M4

[teuben]

It uses <utils/sse.h> which is only implemented with <x86intrin.h>

Since it's a plugin for manipulators, not much is lost by #ifdef'ing the code for non-intel

[teuben]

HAVE_SSE_INSTRUCTIONS is now used as a compiler directive. there will be an autoconf generated method to set this.