atomic: fix CAS with armcc.

On the current code, armcc will fail with:
"libavutil/atomic_gcc.h", line 52: Error:  #2771: first argument must be
a pointer to integer or enumeration type
lavc: remove disabled FF_API_OLD_DECODE_AUDIO cruft
lavc: remove disabled FF_API_OLD_ENCODE_AUDIO cruft
lavc: remove disabled FF_API_OLD_ENCODE_VIDEO cruft
lavc: remove disabled FF_API_MPV_GLOBAL_OPTS cruft
lavc: remove disabled FF_API_COLOR_TABLE_ID cruft
lavc: remove disabled FF_API_INTER_THRESHOLD cruft
lavc: remove disabled FF_API_SUB_ID cruft
lavc: remove disabled FF_API_DSP_MASK cruft
lavc: remove disabled FF_API_FIND_BEST_PIX_FMT cruft
lavc: remove disabled FF_API_CODEC_ID cruft
lavc: remove disabled FF_API_VDA_ASYNC cruft