udf: Move constant to header.
This way, it is a compile time constant and Clang does no longer
complain about dynamic arrays of non-POD types.
Could anyone explain to me the difference? There should not be one.
Whether something is in a header or a source file is completely
irrelevant in C and C++ -- it's the same thing.
It was extern in the header before, defined in one .c file, but referenced
in another to size an array. As a result, the size of that array was only
known at link-time, making it dynamic.
