armemu: Fix FSUBS bug where NaN shouldn't be negated

src/core/arm/skyeye_common/vfp/vfpsingle.cpp

@@ -1148,7 +1148,10 @@ static u32 vfp_single_fsub(ARMul_State* state, int sd, int sn, s32 m, u32 fpscr)
     /*
      * Subtraction is addition with one sign inverted.
      */
-    return vfp_single_fadd(state, sd, sn, vfp_single_packed_negate(m), fpscr);
+    if (m != 0x7FC00000) // Only negate if m isn't NaN.
+        m = vfp_single_packed_negate(m);
+
+    return vfp_single_fadd(state, sd, sn, m, fpscr);
 }
 
 /*