You can change some of the default settings of the compiler for your specific needs.
If you have installed XL C/C++ onto a system running AIX® 5.3, the configuration file is /etc/vac.cfg.53, and if you have installed the compiler onto a system running AIX 6.1, the configuration file is /etc/vac.cfg.61. The GCC options configuration file is /etc/gxlc.cfg.
For more information about how to change the XL C/C++ compiler's settings, see Customizing the configuration file and Configuring the gxlc or gxlc++ option mapping in the XL C/C++ Compiler Reference.