While working on some code that had a large amount of global variables, I wanted to get rid of the global constructor warnings that ensued once I started to use our collections/string classes in these global variables. While the globals will eventually go away in my codebase, there are also constants that would benefit from not having to run constructors.

After having a bit of a look, it seems that as long as there is a constexpr constructor available (which requires that all members are also constexpr-constructible), we can avoid global constructors.

So this is a quick attempt at adding constexpr constructors to the above mentioned classes, as well as the beginnings of supporting this in the Matrix classes as well, however the Matrix attempt is currently blocked by the logic for initializing with the identity matrix, as calling setToIdentity() triggers a warning about this being a C++14 extension.

Similarly the constructor for Common::String has to use an initializer list for the storage array, for which I've seen some comments on StackOverflow that mention that initializing arrays in the initializer list might have problems in some versions of MSVC.

This needs a fair bit of testing across compilers to be sure it doesn't break the compile on some platform, and the overall benefit boils down to being able to create compile time constants of classes that contain these classes.