multimedia/aom: unbreak VMAF after f40d123e50db

ld: error: undefined symbol: environ

referenced by auxv.c:54 (/usr/src/lib/libc/gen/auxv.c:54)

auxv.o:(init_aux_vector_once) in archive /usr/lib/libc.a

referenced by tls.c:443 (/usr/src/lib/libc/gen/tls.c:443)

tls.o:(_init_tls) in archive /usr/lib/libc.a

referenced by getenv.c:250 (/usr/src/lib/libc/stdlib/getenv.c:250)

getenv.o:(__clean_env_destructor) in archive /usr/lib/libc.a

referenced 17 more times

ld: error: undefined symbol: __progname

referenced by getprogname.c:16 (/usr/src/lib/libc/gen/getprogname.c:16)

getprogname.o:(_getprogname) in archive /usr/lib/libc.a

c++: error: linker command failed with exit code 1 (use -v to see invocation)

PR: 255590
Reported by: ice@extreme.hu, fluffy
Regressed by: https://aomedia.googlesource.com/aom/+/b53a4d710849%5E!/