Both files can now be included independently without causing problems.
This also required moving some inline functions into separate files and splitting off the GC definitions from dobject.h to ensure that r_defs does not need to pull in any part of the object hierarchy.
This is one of two places that unconditionally pulled in all Windows headers into the GL code.
We also do not need the cruft for defining the standard integer types. GZDoom is C++11 which means that stdint.h will be present. So the madness with the definitions should be avoided to ensure that the types are always the same.
GLEW has two major problems:
- it always includes everything, there is no way to restrict the header to a specific GL version
- it is mostly broken with a core profile and only works if all sanity checks get switched off.
