You can change some of the default settings of the compiler for your specific needs.
If you are using XL C/C++ on a system running AIX® 6.1, the configuration file is /opt/IBM/xlc/13.1.0/etc/xlc.cfg.61, and if you are on a system running AIX 7.1, the configuration file is /opt/IBM/xlc/13.1.0/etc/xlc.cfg.71. The GCC options configuration file is 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.