To bootstrap GCC all you need is Linux. Crosscompile GCC on Linux to generate a set of binaries and install on AIX. Job done.
I rather doubt binutils supports that particular combination of items
*** Configuration ia64-ibm-aix is obsolete.
*** Specify --enable-obsolete to build it anyway.
*** Support will be REMOVED in the next major release of BINUTILS,
*** unless a maintainer comes forward.