Interpreter: software-based flush-to-zero

bDAZ is now called bFlushToZero to better reflect what it's actually
used for.

I decided not to support any hardware-based flush-to-zero on systems
that don't support this for both inputs _and_ outputs. It makes the code
cleaner and the intersection of CPUs that support SSE2 but not DAZ
should be very small.

Source/Core/Common/Src/MathUtil.h

@@ -64,10 +64,10 @@ inline float FlushToZero(float f)
 	return x.f;
 }
 
-inline double FlushToZeroAsFloat(double d)
+inline double FlushToZero(double d)
 {
 	IntDouble x; x.d = d;
-	if ((x.i & DOUBLE_EXP) < 0x3800000000000000ULL)
+	if ((x.i & DOUBLE_EXP) == 0)
 		x.i &= DOUBLE_SIGN;  // turn into signed zero
 	return x.d;
 }