GCC 5 Release Series Changes, New Features, and Fixes Caveats The default mode for C is now -std=gnu11 instead of -std=gnu89. The C++ runtime library (libstdc++) uses a new ABI by default (see below). The Graphite framework for loop optimizations no longer requires the CLooG library, only ISL version 0.14 (recommended) or 0.12.2. The installation manual contains more information about requirements