audio/cmus: Fix build on powerpc

checking for successful build of ffmpeg.c...
cc1: error: unrecognized command line option "-std=gnu11"
no
configure failed.

track_info.o: In function `track_info_new':
track_info.c:(.text+0x2c): undefined reference to `__atomic_fetch_add_8'

Allow build on powerpc64 again as the error in BROKEN looks to be
same as the first error on powerc.