Starting with GHC 8.0 it is possible again to build GHC on IBM AIX
This page documents which hoops to jump through to make this happen and what the current limitations are.
The AIX Open Source Packages repository is a convenient source to get the prerequisites.
A consequence of this is that building a GHC crosscompiler targetting AIX is quite difficult.
Sadly (at the time of writing), binutils's ld has only partial support for AIX. IBM's ld must be used. Also, IBM's ar is recommended over binutils's.
Having said that, IBM's as has deficiencies which cause problems when compiling GHC. So gas from binutils is recommended for building GHC.