mips/asmdefs: use _ABI64 as defined by gcc

Unfortunately android < api 21 (lollipop) doesn't have the sgidefs.h header,
the easiest way around this is to just use the preprocessor definitions from
gcc / clang.
Signed-off-by: James Cowgill <james410@cowgill.org.uk>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/mips/asmdefs.h

@@ -27,9 +27,7 @@
 #ifndef AVUTIL_MIPS_ASMDEFS_H
 #define AVUTIL_MIPS_ASMDEFS_H
 
-#include <sgidefs.h>
-
-#if _MIPS_SIM == _ABI64
+#if defined(_ABI64) && _MIPS_SIM == _ABI64
 # define PTRSIZE        " 8 "
 # define PTRLOG         " 3 "
 # define PTR_ADDU       "daddu "