Have you built gcc on AIX 4.x? Personally? Not recently. I've done so in the past.
The person who builds the AIX binaries for TL is Vladimir Volovich. As I recall, vvv told me that he did have gcc on AIX, but that the resulting binaries were both slower and bigger than the IBM C compiler results. There may also have been more issues of portability between AIX versions. These were the "various reasons". (I encouraged him to use gcc anyway.) Anyway, my point here was merely that decl-after-stmt was not an unreasonable assumption for GNU packages.