Rant on C libraries
C99 features don't make sense in C header files, and I don't know why they do it. I often am writing projects in ANSI C with pedantic warnings, and some libraries make the compiler light up with warnings.
In most cases, it wouldn't take much effort to make offending header files ANSI compliant. The JACK api, for instance, only needs to remove C++ style comments and commas at the end of enumerators. (almost tempted to make a PR for this one).