I created a Projucer project on Linux and copied the Source/ & JuceLibraryCode/ to the BSD machine. After applying my patch to the JUCE code, the compilation of a static library works without any problems. I’m currently using CMake to build things, but I’m stuck on multiple link errors when trying to create the executable (CMake finds the includes during compilation but not the libraries for linking). I will try with manually building things sometime this week.
I admit that my knowledge about FreeBSD is extremely limited, though I’m totally open to learning more about it.
Some quick searching online shows that these macros exist in glibc the same as uClibc, so it’s entirely possible my message applies similarly: where some kind of configuration for glibc has the locale contents disabled - although I can be totally wrong about that.