Interpreter_FPUtils: Set FPSCR.VXSNAN if any operand to NI_madd is a signaling NaN

If any operand is a signaling NaN, we need to signify this by setting
the VXSNAN bit.

Fixes NaN flag setting for fmadd, fmadds, fnmadd, fnmadds, ps_madd,
ps_nmadd, ps_madds0, and ps_madds1

Source/Core/Core/PowerPC/Interpreter/Interpreter_FPUtils.h

@@ -190,25 +190,37 @@ inline double NI_sub(double a, double b)
 inline double NI_madd(double a, double c, double b)
 {
   double t = a * c;
+
   if (std::isnan(t))
   {
+    if (Common::IsSNAN(a) || Common::IsSNAN(b) || Common::IsSNAN(c))
+      SetFPException(FPSCR_VXSNAN);
+
     if (std::isnan(a))
       return MakeQuiet(a);
     if (std::isnan(b))
       return MakeQuiet(b);  // !
     if (std::isnan(c))
       return MakeQuiet(c);
+
     SetFPException(FPSCR_VXIMZ);
     return PPC_NAN;
   }
+
   t += b;
+
   if (std::isnan(t))
   {
+    if (Common::IsSNAN(b))
+      SetFPException(FPSCR_VXSNAN);
+
     if (std::isnan(b))
       return MakeQuiet(b);
+
     SetFPException(FPSCR_VXISI);
     return PPC_NAN;
   }
+
   return t;
 }