avutil/mem: Add DECLARE_ASM_ALIGNED macro for DJGPP architecture.

The macro was added in 43171a2a, but I forgot to add it to the DJGPP architecture in that change.
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavutil/mem.h

@@ -106,6 +106,7 @@
     #define DECLARE_ASM_CONST(n,t,v)    const t __attribute__ ((aligned (n))) v
 #elif defined(__DJGPP__)
     #define DECLARE_ALIGNED(n,t,v)      t __attribute__ ((aligned (FFMIN(n, 16)))) v
+    #define DECLARE_ASM_ALIGNED(n,t,v)  t av_used __attribute__ ((aligned (FFMIN(n, 16)))) v
     #define DECLARE_ASM_CONST(n,t,v)    static const t av_used __attribute__ ((aligned (FFMIN(n, 16)))) v
 #elif defined(__GNUC__) || defined(__clang__)
     #define DECLARE_ALIGNED(n,t,v)      t __attribute__ ((aligned (n))) v