To run on ancient CPUs, we compile for Windows with -arch:SSE since
8bd6bf93 (August 2014). Thus
_M_IX86_FP gets defined as 1. This meant that LO_SSE2_AVAILABLE did
not get defined, and that we hardcoded tools::cpuid::hasSSE2() as
always returning false. That was hardly the intent.

Change-Id: I7ee34510a774dab865c8990b74b91a5284218a96