GCC 14 has made changes to support new standards, fixing bugs and intentionally changing behaviors. Some common C language issues have been addressed, such as certain warnings now being treated as errors, and function prototyping being added for type checking. Compatibility has been improved, but some programs may need updates to address historic C compatibility issues. New warnings have been introduced to catch typos in function prototypes and incorrect uses of return statements. Additionally, GCC now enforces type checking on pointer types and restricts implicit casting. The impact on Autoconf and build environment probing is also discussed. These changes may require adjustments for C++ programs as well.
https://gcc.gnu.org/gcc-14/porting_to.html#c