At the moment of writing, AIX supports two different native C compilers,
for which you have to pay: B<xlC> and B<vac>. If you decide to use either
of these two (which is quite a lot easier than using gcc), be sure to
upgrade to the latest available patch level. Currently:

    xlC.C     3.1.4.10 or 3.6.6.0 or 4.0.2.2 or 5.0.2.9 or 6.0.0.3
    vac.C     4.4.0.3  or 5.0.2.6 or 6.0.0.1