The following sets of software are required to build Ruby 1.8.4 on AIX, using GCC or IBM VaC. The only non-free piece of software is the IBM Visual Age for C Compiler (VaC), which must be purchased and licensed from IBM if you choose to use it. Otherwise, the recommended way to build Ruby is with the GNU Compiler Collection (GCC).
GNU Compiler Collection. You must have at least GCC 3.3.2 installed on your system and the associated library files:
gcc-3.3.2-5.aix5.X.ppc.rpm
gcc-cplusplus-3.3.2-5.aix5.X.ppc.rpm
libgcc-3.3.2-5.aix5.X.ppc.rpm
libstdcplusplus-3.3.2-5.aix5.X.ppc.rpm
libstdcplusplus-devel-3.3.2-5.aix5.X.ppc.rpm
GCC and the other libraries listed below are available from the AIX Toolbox for Linux website.
OPTIONAL: IBM Visual Age for C Compiler. This is not needed if you have the correct version of GCC installed. But, for those that must use VaC, here are the requirements. For AIX 5.3 you must have version 7.0 of the VaC compiler. I have not tested with VaC 6.0, but I have tested with as low as versions 3.5 on AIX 4.3.3 with success. Therefore, I suspect it will work just fine with 6.0.
OpenSSL 0.9.7. Binary and development files are needed. OpenSSL is found on the cryptographic tools link on the right hand side of their AIX Toolbox for Linux page. Note that you will need a free IBM userid and password to download from their "cryptographic" download section. As of this writing, OpenSSL 0.9.7g is the current release for AIX 5L; however, only OpenSSL 0.9.6m is available for AIX 4.3.3. If you must use AIX 4.3.3, this is your only option outside of building it yourself, unfortunately, 0.9.6m does not work with some Ruby Gems (particularly the Net::SSH release).
zlib. Binary and development files. Again, these are available from the AIX Toolbox for Linux page.
readline. Binary and development files for GNU Readline support. This allows you to use common keyboard navigation inside irb.
GNU Make. Binary only. The make command that ships with AIX cannot handle GNU-style Makefiles, so GNU Make must be used. Again, this is available on the AIX Toolbox for Linux page at IBM.
OPTIONAL: If using AIX 5.1 or AIX 4.3.3, you will also need to download the prngd binaries. These older versions of AIX do not have built-in random number generators or devices like /dev/urandom or /dev/random. OpenSSL requires these devices to generate seeds for encryption. If you have one of these versions of AIX you must install the Pseudo Random Number Generator from the AIX Toolbox for Linux page.