Prevent multiple evaluation of macro argument.

Index: fixed.h
--- fixed.h.orig
+++ fixed.h
@@ -358,15 +358,15 @@ mad_fixed_t mad_f_mul_inline(mad_fixed_t x, mad_fixed_
  * significant bit depends on OPT_ACCURACY via mad_f_scale64().
  */
 #  define MAD_F_MLX(hi, lo, x, y)  \
-    do {  \
+   ({ mad_fixed_t __x = (x);  \
+      mad_fixed_t __y = (y);  \
       asm ("mullw %0,%1,%2"  \
 	   : "=r" (lo)  \
-	   : "%r" (x), "r" (y));  \
+	   : "%r" (__x), "r" (__y));  \
       asm ("mulhw %0,%1,%2"  \
 	   : "=r" (hi)  \
-	   : "%r" (x), "r" (y));  \
-    }  \
-    while (0)
+	   : "%r" (__x), "r" (__y));  \
+   })
 
 #  if defined(OPT_ACCURACY)
 /*