It might very well be a bug in your preprocessor or compiler:

$ oslevel
5.2.0.0
$ oslevel -r
5200-04
$ lslpp -l xlC.rte
  Fileset                      Level  State      Description
  --------------------------------------------------------------------
+--------
Path: /usr/lib/objrepos
  xlC.rte                    9.0.0.9  COMMITTED  XL C/C++ Runtime
$
[download]

From the file README.aix (perldoc paerlaix), it says:

At the moment of writing, AIX supports two different native C compiler
+s,
for which you have to pay: B<xlC> and B<vac>. If you decide to use eit
+her
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
[download]

Which is already rather outdated now, but most likely 6.0.0.0 is insufficient and you should up to at least 6.0.0.3.