Test for SSE2 at run-time on Windows

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

include/tools/cpuid.hxx

@@ -16,7 +16,7 @@
 
 #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__)) && defined(__SSE2__)
 #define LO_SSE2_AVAILABLE 1
-#elif defined(_MSC_VER) && (defined(_M_AMD64) || (defined(_M_IX86) && defined(_M_IX86_FP) && _M_IX86_FP >= 2))
+#elif defined(_MSC_VER)
 #define LO_SSE2_AVAILABLE 1
 #endif