Computations on NaNs are supposed to return one of the input NaNs unchanged.

Fix a few places in the sparc64 floating-point emulator where this wasn't
being handled properly.

Submitted by:	bde

lib/libc/sparc64/fpu/fpu_emu.h

@@ -159,7 +159,8 @@ struct fpemu {
  * Each of these may modify its inputs (f1,f2) and/or the temporary.
  * Each returns a pointer to the result and/or sets exceptions.
  */
-#define	__fpu_sub(fe) ((fe)->fe_f2.fp_sign ^= 1, __fpu_add(fe))
+#define	__fpu_sub(fe)	(ISNAN(&(fe)->fe_f2) ? 0 : ((fe)->fe_f2.fp_sign ^= 1), \
+			    __fpu_add(fe))
 
 #ifdef FPU_DEBUG
 #define	FPE_INSN	0x1

lib/libc/sparc64/fpu/fpu_mul.c

@@ -125,10 +125,8 @@ __fpu_mul(fe)
 	 *	The result is x * y (XOR sign, multiply bits, add exponents).
 	 */
 	ORDER(x, y);
-	if (ISNAN(y)) {
-		y->fp_sign ^= x->fp_sign;
+	if (ISNAN(y))
 		return (y);
-	}
 	if (ISINF(y)) {
 		if (ISZERO(x))
 			return (__fpu_newnan(fe));