Look into memory usage of compiling QtProtobuf generated files

QtProtobuf generated sources take a lot of memory to compile on my local machine, some individual files take up to 3GB when building combined with MSVC.

Need to investigate if this is consistent across platforms and then try to figure out ways to reduce the memory usage.

One potential way may be to forego building the files as OBJ-libraries and rather use dynamic or static libraries. Some experimentation needed.