ao.m4 has a few problems for cross-compile environments, notably buildroot.
Namely:
elif test "x$prefix" != "xNONE"; then
AO_LIBS="-L$prefix/lib"
and
elif test "x$prefix" != "xNONE"; then
AO_CFLAGS="-I$prefix/include"
Prefix is only valid on target. It should not be used on host.
],, no_ao=yes,[echo $ac_n "cross compiling; assumed OK... $ac_c"])
Well, its not OK to "assume OK". AC_TRY_RUN() should be avoided. I think the generic AC_CHECK_HEADERS()+ AC_CHECK_LIBS() should do quite fine.