Bug#1039482: gcc-9-cross: Update to autoconf2.69

[Bastian Germann]

Source: gcc-9-cross
Version: 27

Please update the autoconf2.64 build dependency to autoconf2.69 which is also 
implied by gcc-9-source.
I am going to update the other of the last two autoconf2.64 reverse 
dependencies,
so resolving this enables dropping autoconf2.64 from the archive.