Restore _MSC_VER case in DECLARE_ALIGNED/DECLARE_ASM_CONST macro declaration.

This compiler might be supported in the future or we might some day decide
to export these macros.

Originally committed as revision 16786 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavutil/internal.h

@@ -264,6 +264,9 @@ if((y)<(x)){\
 #elif defined(__GNUC__)
     #define DECLARE_ALIGNED(n,t,v)      t v __attribute__ ((aligned (n)))
     #define DECLARE_ASM_CONST(n,t,v)    static const t v attribute_used __attribute__ ((aligned (n)))
+#elif defined(_MSC_VER)
+    #define DECLARE_ALIGNED(n,t,v)      __declspec(align(n)) t v
+    #define DECLARE_ASM_CONST(n,t,v)    __declspec(align(n)) static const t v
 #elif HAVE_INLINE_ASM
     #error The asm code needs alignment, but we do not know how to do it for this compiler.
 #else