intreadwrite: Dont evaluate value for AV_W* multiple times.

Evaluating it multiple times, can have side effects and is possibly slow.
So its definitly a bad idea.
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/intreadwrite.h

@@ -210,7 +210,8 @@ union unaligned_16 { uint16_t l; } __attribute__((packed)) av_alias;
       ((const uint8_t*)(x))[1])
 #endif
 #ifndef AV_WB16
-#   define AV_WB16(p, d) do {                   \
+#   define AV_WB16(p, darg) do {                \
+        unsigned d = (darg);                    \
         ((uint8_t*)(p))[1] = (d);               \
         ((uint8_t*)(p))[0] = (d)>>8;            \
     } while(0)
@@ -222,7 +223,8 @@ union unaligned_16 { uint16_t l; } __attribute__((packed)) av_alias;
       ((const uint8_t*)(x))[0])
 #endif
 #ifndef AV_WL16
-#   define AV_WL16(p, d) do {                   \
+#   define AV_WL16(p, darg) do {                \
+        unsigned d = (darg);                    \
         ((uint8_t*)(p))[0] = (d);               \
         ((uint8_t*)(p))[1] = (d)>>8;            \
     } while(0)
@@ -236,7 +238,8 @@ union unaligned_16 { uint16_t l; } __attribute__((packed)) av_alias;
                 ((const uint8_t*)(x))[3])
 #endif
 #ifndef AV_WB32
-#   define AV_WB32(p, d) do {                   \
+#   define AV_WB32(p, darg) do {                \
+        unsigned d = (darg);                    \
         ((uint8_t*)(p))[3] = (d);               \
         ((uint8_t*)(p))[2] = (d)>>8;            \
         ((uint8_t*)(p))[1] = (d)>>16;           \
@@ -252,7 +255,8 @@ union unaligned_16 { uint16_t l; } __attribute__((packed)) av_alias;
                 ((const uint8_t*)(x))[0])
 #endif
 #ifndef AV_WL32
-#   define AV_WL32(p, d) do {                   \
+#   define AV_WL32(p, darg) do {                \
+        unsigned d = (darg);                    \
         ((uint8_t*)(p))[0] = (d);               \
         ((uint8_t*)(p))[1] = (d)>>8;            \
         ((uint8_t*)(p))[2] = (d)>>16;           \
@@ -272,7 +276,8 @@ union unaligned_16 { uint16_t l; } __attribute__((packed)) av_alias;
       (uint64_t)((const uint8_t*)(x))[7])
 #endif
 #ifndef AV_WB64
-#   define AV_WB64(p, d) do {                   \
+#   define AV_WB64(p, darg) do {                \
+        uint64_t d = (darg);                    \
         ((uint8_t*)(p))[7] = (d);               \
         ((uint8_t*)(p))[6] = (d)>>8;            \
         ((uint8_t*)(p))[5] = (d)>>16;           \
@@ -296,7 +301,8 @@ union unaligned_16 { uint16_t l; } __attribute__((packed)) av_alias;
       (uint64_t)((const uint8_t*)(x))[0])
 #endif
 #ifndef AV_WL64
-#   define AV_WL64(p, d) do {                   \
+#   define AV_WL64(p, darg) do {                \
+        uint64_t d = (darg);                    \
         ((uint8_t*)(p))[0] = (d);               \
         ((uint8_t*)(p))[1] = (d)>>8;            \
         ((uint8_t*)(p))[2] = (d)>>16;           \